Method for manufacturing light emitting device

ABSTRACT

An object of the present invention to improve reliability of a light emitting device having a mixed layer including an organic compound and metal oxide without reducing productivity. The above object is solved in such a way that after forming the mixed layer including the organic compound and metal oxide, the mixed layer is exposed to a nitrogen gas atmosphere without being exposed to a gas atmosphere including oxygen, and then a stacked film is formed over the mixed layer without exposing the mixed layer to a gas atmosphere including oxygen.

This application is a divisional of copending application Ser. No.11/455,254 filed on Jun. 16, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing anelectroluminescence light emitting device used for a planar light sourceor a display element (hereinafter, also referred to as a “light emittingdevice”).

2. Description of the Related Art

An electroluminescence light emitting device has a light emitting layerformed using an organic compound and the like. Such anelectroluminescence light emitting device is attracting attention forrealizing a large-area display element at low driving voltage.

To improve efficiency of an element, Tang et al. proposed a structure inwhich organic compounds having different carrier transporting propertiesare stacked to inject holes and electrons from an anode electrode layerand a cathode electrode layer with good balance. Further, a thickness ofan organic layer is set to be 200 nm or less to realize light emittingluminance of 1,000 cd/m² and external quantum efficiency of 1% atapplied voltage of 10 V or less (for example, non-patent document 1).

In developing such a high-efficiency element, it has been recognizedthat a technique for injecting electrons from a cathode electrode layeror holes from an anode electrode layer to an organic layer withoutgenerating an energy barrier, is an essential element.

Kido et al. proposed that a hole injecting layer is formed by a mixedlayer of metal oxide and an organic compound. According to Kido et al.,this can reduce driving voltage of an element and drastically reducerisk of electrical short between a cathode electrode layer and an anodeelectrode layer by adjusting a thickness of the hole transporting layerwithout increasing driving voltage (patent document 1).

However, there has been a problem of shortening luminance half life inthe above described structures (patent document 2).

-   [Non patent document 1]: Applied Physics Letter., 51, 913 (1987)-   [Patent document 1]: Japanese Patent Application Laid-Open No.    2005-123095-   [Patent document 2]: Japanese Patent Application Laid-Open No.    2005-166641-   [Patent document 3]: Japanese Patent Application Laid-Open No.    2000-68068-   [Patent document 4]: Japanese Patent Application Laid-Open No. Hei    11-8065

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to improvereliability of a light, emitting device having a mixed layer includingan organic compound and metal oxide without reducing productivity. Thepresent invention solves the above described problem in such a way thatafter forming a mixed layer including an organic compound and metaloxide, the mixed layer is exposed to a nitrogen (N₂) gas atmospherewithout being exposed to a gas atmosphere including oxygen, and then astacked film is formed without exposing the mixed layer to a gasatmosphere including oxygen. The gas atmosphere including oxygenindicates a gas atmosphere including an oxygen atom such as oxygen gas,NO₂ gas, N₂O gas or the like. After the formation of the mixed layerincluding the organic compound and metal oxide, by exposing the mixedlayer to the nitrogen (N₂) gas atmosphere without being exposed to a gasatmosphere including oxygen, film quality and reliability are improvedwithout reducing productivity.

In an aspect of the present invention, an anode is formed; a mixed layerincluding an organic compound and metal oxide is formed over the anode;the mixed layer is exposed to a nitrogen gas atmosphere without beingexposed to a gas atmosphere including oxygen; a hole transporting layeris formed over the mixed layer without exposing the mixed layer to a gasatmosphere including oxygen; a light emitting layer is formed over thehole transporting layer; and a cathode is formed over the light emittinglayer.

In another aspect of the present invention, an anode is formed; a firstmixed layer including an organic compound and metal oxide is formed overthe anode; the first mixed layer is exposed to a nitrogen gas atmospherewithout being exposed to a gas atmosphere including oxygen; a secondmixed layer including an organic compound and metal oxide is formed overthe first mixed layer without exposing the first mixed layer to a gasatmosphere including oxygen; the second mixed layer is exposed to anitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen; a hole transporting layer is formed over the secondmixed layer without exposing the second mixed layer to a gas atmosphereincluding oxygen; a light emitting layer is formed over the holetransporting layer; and a cathode is formed over the light emittinglayer.

In another aspect of the present invention, an anode is formed; a holetransporting layer is formed over the anode; a light emitting layer isformed over the hole transporting layer; an electron transporting layeris formed over the light emitting layer; a mixed layer including anorganic compound and metal oxide is formed over the electrontransporting layer; the mixed layer is exposed to a nitrogen gasatmosphere without being exposed to a gas atmosphere including oxygen;and a cathode is formed over the mixed layer without exposing the mixedlayer to a gas atmosphere including oxygen.

In another aspect of the present invention, an anode is formed; a holetransporting layer is formed over the anode; a light emitting layer isformed over the hole transporting layer; an electron transporting layeris formed over the light emitting layer; a first mixed layer includingan organic compound and metal oxide is formed over the electrontransporting layer; the first mixed layer is exposed to a nitrogen gasatmosphere without being exposed to a gas atmosphere including oxygen; asecond mixed layer including an organic compound and metal oxide isformed over the first mixed layer without exposing the first mixed layerto a gas atmosphere including oxygen; the second mixed layer is exposedto a nitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen; and a cathode is formed over the second mixed layerwithout exposing the second mixed layer to a gas atmosphere includingoxygen.

The anode, the hole transporting layer, the light emitting layer, themixed layer, the first mixed layer, the second mixed layer, the electrontransporting layer, and the cathode are desirably formed in vacuum orunder reduced pressure.

The mixed layer may be formed after the anode is subjected to heattreatment. The heat treatment is desirably performed in vacuum or underreduced pressure.

An electron injecting layer may be formed between the mixed layer andthe electron transporting layer. The electron injecting layer isdesirably formed in vacuum or under reduced pressure.

After the mixed layer, the first mixed layer, and the second mixed layerare exposed to a nitrogen gas atmosphere, the nitrogen gas may beevacuated, and then they may be exposed to a nitrogen gas atmosphereagain.

The mixed layer, the first mixed layer, and the second mixed layer maybe sprayed with nitrogen gas so as to be exposed to a nitrogen gasatmosphere.

In another aspect of the present invention, a cathode is formed; a mixedlayer including an organic compound and metal oxide is formed over thecathode; the mixed layer is exposed to a nitrogen gas atmosphere withoutbeing exposed to a gas atmosphere including oxygen; an electrontransporting layer is formed over the mixed layer without exposing themixed layer to a gas atmosphere including oxygen; a light emitting layeris formed over the electron transporting layer; and an anode is formedover the light emitting layer.

In another aspect of the present invention, a cathode is formed; a firstmixed layer including an organic compound and metal oxide is formed overthe cathode; the first mixed layer is exposed to a nitrogen gasatmosphere without being exposed to a gas atmosphere including oxygen; asecond mixed layer including an organic compound and metal oxide isformed over the first mixed layer without exposing the first mixed layerto a gas atmosphere including oxygen; the second mixed layer is exposedto a nitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen; an electron transporting layer is formed over thesecond mixed layer without exposing the second mixed layer to a gasatmosphere including oxygen; a light emitting layer is formed over theelectron transporting layer; a hole transporting layer is formed overthe light emitting layer; and an anode is formed over the holetransporting layer.

In another aspect of the present invention, a cathode is formed; a mixedlayer including an organic compound and metal oxide is formed over thecathode; the mixed layer is exposed to a nitrogen gas atmosphere withoutbeing exposed to a gas atmosphere including oxygen; an electroninjecting layer is formed over the mixed layer without exposing themixed layer to a gas atmosphere including oxygen; an electrontransporting layer is formed over the electron injecting layer; a lightemitting layer is formed over the electron transporting layer; a holetransporting layer is formed over the light emitting layer; and an anodeis formed over the hole transporting layer.

In another aspect of the present invention, a cathode is formed; a firstmixed layer including an organic compound and metal oxide is formed overthe cathode; the first mixed layer is exposed to a nitrogen gasatmosphere without being exposed to a gas atmosphere including oxygen; asecond mixed layer including an organic compound and metal oxide isformed over the first mixed layer without exposing the first mixed layerto a gas atmosphere including oxygen; the second mixed layer is exposedto a nitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen; an electron injecting layer is formed over the secondmixed layer without exposing the second mixed layer to a gas atmosphereincluding oxygen; an electron transporting layer is formed over theelectron injecting layer; a light emitting layer is formed over theelectron transporting layer; and an anode is formed over the lightemitting layer.

In another aspect of the present invention, a cathode is formed; anelectron transporting layer is formed over the cathode; a light emittinglayer is formed over the electron transporting layer; a holetransporting layer is formed over the light emitting layer; a mixedlayer including an organic compound and metal oxide is formed over thehole transporting layer; the mixed layer is exposed to a nitrogen gasatmosphere without being exposed to a gas atmosphere including oxygen;and an anode is formed over the mixed layer without exposing the mixedlayer to a gas atmosphere including oxygen.

In another aspect of the present invention, a cathode is formed; anelectron transporting layer is formed over the cathode; a light emittinglayer is formed over the electron transporting layer; a holetransporting layer is formed over the light emitting layer; a firstmixed layer including an organic compound and metal oxide is formed overthe hole transporting layer; the first mixed layer is exposed to anitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen; a second mixed layer including an organic compound andmetal oxide is formed over the first mixed layer without exposing thefirst mixed layer to a gas atmosphere including oxygen; the second mixedlayer is exposed to a nitrogen gas atmosphere without being exposed to agas atmosphere including oxygen; and an anode is formed over the secondmixed layer without exposing the second mixed layer to a gas atmosphereincluding oxygen.

The anode, the hole transporting layer, the light emitting layer, themixed layer, the first mixed layer, the second mixed layer, the electrontransporting layer, the electron injecting layer, and the cathode aredesirably formed in vacuum or under reduced pressure.

After the mixed layer, the first mixed layer, and the second mixed layerare exposed to a nitrogen gas atmosphere, the nitrogen gas may beevacuated, and then they may be exposed to a nitrogen gas atmosphereagain.

The mixed layer, the first mixed layer, and the second mixed layer maybe sprayed with the nitrogen gas so as to be exposed to a nitrogen gasatmosphere.

In another aspect of the present invention, an anode is formed; a firstmixed layer including an organic compound and metal oxide is formed overthe anode; the first mixed layer is exposed to a nitrogen gas atmospherewithout being exposed to a gas atmosphere including oxygen; a holetransporting layer is formed over the first mixed layer without exposingthe first mixed layer to a gas atmosphere including oxygen; a lightemitting layer is formed over the hole transporting layer; an electrontransporting layer is formed over the light emitting layer; a secondmixed layer including an organic compound and metal oxide is formed overthe electron transporting layer; the second mixed layer is exposed to anitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen; and a cathode is formed over the second mixed layerwithout exposing the second mixed layer to a gas atmosphere includingoxygen.

The first mixed layer may be formed after the anode is subjected to heattreatment. The heat treatment is desirably performed in vacuum or underreduced pressure.

An electron injecting layer may be formed between the second mixed layerand the electron transporting layer.

The anode, the hole transporting layer, the light emitting layer, themixed layer, the first mixed layer, the second mixed layer, the electrontransporting layer, the electron injecting layer, and the cathode aredesirably formed in vacuum or under reduced pressure.

In another aspect of the present invention, a cathode is formed; a firstmixed layer including an organic compound and metal oxide is formed overthe cathode; the first mixed layer is exposed to a nitrogen gasatmosphere without being exposed to a gas atmosphere including oxygen;an electron transporting layer is formed over the first mixed layerwithout exposing the first mixed layer to a gas atmosphere includingoxygen; a light emitting layer is formed over the electron transportinglayer; a hole transporting layer is formed over the light emittinglayer; a second mixed layer including an organic compound and metaloxide is formed over the hole transporting layer; the second mixed layeris exposed to a nitrogen gas atmosphere without being exposed to a gasatmosphere including oxygen; and an anode is formed over the secondmixed layer without exposing the second mixed layer to a gas atmosphereincluding oxygen.

In another aspect of the present invention, a cathode is formed; a firstmixed layer including an organic compound and metal oxide is formed overthe cathode; the first mixed layer is exposed to a nitrogen gasatmosphere without being exposed to a gas atmosphere including oxygen;an electron injecting layer is formed over the first mixed layer withoutexposing the first mixed layer to a gas atmosphere including oxygen; anelectron transporting layer is formed over the electron injecting layer;a light emitting layer is formed over the electron transporting layer; ahole transporting layer is formed over the light emitting layer; asecond mixed layer including an organic compound and metal oxide isformed over the hole transporting layer; the second mixed layer isexposed to a nitrogen gas atmosphere without being exposed to a gasatmosphere including oxygen; and an anode is formed over the secondmixed layer without exposing the second mixed layer to a gas atmosphereincluding oxygen.

After the first mixed layer is exposed to the nitrogen gas atmosphere,the nitrogen gas may be evacuated, and then the first mixed layer may beexposed to a nitrogen gas atmosphere again. After the second mixed layeris exposed to the nitrogen gas atmosphere, the nitrogen gas may beevacuated, and then the second mixed layer may be exposed to a nitrogengas atmosphere again.

The first mixed layer and the second mixed layer may be sprayed with thenitrogen gas so as to be exposed to the nitrogen gas atmosphere.

The anode, the hole transporting layer, the light emitting layer, themixed layer, the first mixed layer, the second mixed layer, the electrontransporting layer, the electron injecting layer, and the cathode aredesirably formed in vacuum or under reduced pressure.

The first mixed layer may be formed by stacking a third mixed layerincluding an organic compound and metal oxide and a fourth mixed layerincluding an organic compound and metal oxide. Further, the second mixedlayer may be formed by stacking a fifth mixed layer including an organiccompound and metal oxide and a sixth mixed layer including an organiccompound and metal oxide.

In this case, the third mixed layer may be formed and the third mixedlayer may be exposed to a nitrogen gas atmosphere without being exposedto a gas atmosphere including oxygen. Subsequently, the fourth mixedlayer may be formed without exposing the third mixed layer to a gasatmosphere including oxygen, the fourth mixed layer may be exposed to anitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen, and then a subsequent layer may be formed withoutexposing the third mixed layer to a gas atmosphere including oxygen.

Further, the fifth mixed layer may be formed and the fifth mixed layermay be exposed to a nitrogen gas atmosphere without being exposed to agas atmosphere including oxygen. Subsequently, the sixth mixed layer maybe formed without exposing the fifth mixed layer to a gas atmosphereincluding oxygen, the sixth mixed layer may be exposed to a nitrogen gasatmosphere without being exposed to a gas atmosphere including oxygen,and then a subsequent layer may be formed without exposing the sixthmixed layer to a gas atmosphere including oxygen.

After the third mixed layer is exposed to the nitrogen gas atmosphere,the nitrogen gas may be evacuated, and then the third mixed layer may beexposed to a nitrogen gas atmosphere again. After the fourth mixed layeris exposed to the nitrogen gas atmosphere, the nitrogen gas may beevacuated, and then the fourth mixed layer may be exposed to a nitrogengas atmosphere again.

After the fifth mixed layer is exposed to the nitrogen gas atmosphere,the nitrogen gas may be evacuated, and then the fifth mixed layer may beexposed to a nitrogen gas atmosphere again. After the sixth mixed layeris exposed to the nitrogen gas atmosphere, the nitrogen gas may beevacuated, and then the sixth mixed layer may be exposed to a nitrogengas atmosphere again.

The third mixed layer and the fourth mixed layer may be sprayed withnitrogen gas so as to be exposed to a nitrogen gas atmosphere.

The fifth mixed layer and the sixth mixed layer may be sprayed withnitrogen gas so as to be exposed to a nitrogen gas atmosphere.

In another aspect of the present invention, an anode is formed; a firstlight emitting unit including a light emitting layer is formed over theanode; a layer including a substance having an electron donatingproperty and a substance having an electron transporting property isformed over the first light emitting unit; a mixed layer including anorganic compound and metal oxide is formed over the layer including thesubstance having the electron donating property and the substance havingthe electron transporting property; the mixed layer is exposed to anitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen; a second light emitting unit is formed over the mixedlayer without exposing the mixed layer to a gas atmosphere includingoxygen; and a cathode is formed over the second light emitting unit.

In another aspect of the present invention, an anode is formed; a firstlight emitting unit including a light emitting layer is formed over theanode; a layer including a substance having an electron donatingproperty and a substance having an electron transporting property isformed over the first light emitting unit; a first mixed layer includingan organic compound and metal oxide is formed over the layer includingthe substance having the electron donating property and the substancehaving the electron transporting property; the first mixed layer isexposed to a nitrogen gas atmosphere without being exposed to a gasatmosphere including oxygen; a second mixed layer is formed over thefirst mixed layer without exposing the first mixed layer to a gasatmosphere including oxygen; the second mixed layer is exposed to anitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen; a second light emitting unit is formed over the secondmixed layer without exposing the second mixed layer to a gas atmosphereincluding oxygen; and a cathode is formed over the second light emittingunit.

In another aspect of the present invention, a cathode is formed; a firstlight emitting unit including a light emitting layer is formed over thecathode; a layer including a substance having an electron donatingproperty and a substance having an electron transporting property isformed over the first light emitting unit; a mixed layer including anorganic compound and metal oxide is formed over the layer including thesubstance having the electron donating property and the substance havingthe electron transporting property; the mixed layer is exposed to anitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen; a second light emitting unit is formed over the mixedlayer without exposing the mixed layer to a gas atmosphere includingoxygen; and an anode is formed over the second light emitting unit.

In another aspect of the present invention, a cathode is formed; a firstlight emitting unit including a light emitting layer is formed over thecathode; a layer including a substance having an electron donatingproperty and a substance having an electron transporting property isformed over the first light emitting unit; a first mixed layer includingan organic compound and metal oxide is formed over the layer includingthe substance having the electron donating property and the substancehaving the electron transporting property; the first mixed layer isexposed to a nitrogen gas atmosphere without being exposed to a gasatmosphere including oxygen; a second mixed layer is formed over thefirst mixed layer without exposing the first mixed layer to a gasatmosphere including oxygen; the second mixed layer is exposed to anitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen; a second light emitting unit is formed over the secondmixed layer without exposing the second mixed layer to a gas atmosphereincluding oxygen; and an anode is formed over the second light emittingunit.

After the mixed layer is exposed to a nitrogen gas atmosphere, thenitrogen gas may be evacuated, and then it may be exposed to a nitrogengas atmosphere again.

The mixed layer may be sprayed with the nitrogen gas so as to be exposedto a nitrogen gas atmosphere.

After the anode is subjected to heat treatment, the light emitting unitsmay be formed. The heat treatment is desirably performed in vacuum orunder reduced pressure.

Each light emitting unit includes the light emitting layer. An electrontransporting layer and a hole transporting layer may be formed in thelight emitting unit. Further, an electron injecting layer may be formedbetween the cathode and the electron transporting layer. A holeinjecting layer may be formed between the anode and the holetransporting layer.

After the first mixed layer and the second mixed layer are exposed tothe nitrogen gas atmosphere, the nitrogen gas may be evacuated, and thenthey may be exposed to a nitrogen gas atmosphere again.

The first mixed layer and the second mixed layer may be sprayed withnitrogen gas so as to be exposed to a nitrogen gas atmosphere.

The anode, the light emitting unit, the mixed layer, the first mixedlayer, the second mixed layer, and the cathode are desirably formed invacuum or under reduced pressure.

When treatment for exposing to the nitrogen gas atmosphere is performed,it is preferably performed at a room temperature without heating. Whenheating, a characteristic is easily changed so that it is thought that acharacteristic of a light emitting device is easily varied. Further, theamount of moisture contained in the nitrogen gas is set to be 40 ppm orless, and preferably, 3 ppm or less.

Ogawa et al. proposed a technique in which after forming a CuPc organicfilm having a hole injecting property, the CuPc organic film issubjected to first gas rinse treatment with N₂ gas, and then second gasrinse treatment is performed with NO₂ gas such that the NO₂ gaspermeates the CuPc organic film (the patent document 3). In the presentinvention, however, after forming the mixed layer, the mixed layer isexposed to the nitrogen gas atmosphere without being exposed to a gasatmosphere including oxygen, and then a stacked film is formed withoutbeing exposed to a gas atmosphere including oxygen. Therefore, thepresent invention is completely different from the patent document 3 inwhich the first gas rinse treatment is performed with the N₂ gas andthen the organic film is exposed to a gas atmosphere including oxygen.

Further, Kuribayashi et al. proposed a technique in which when organicelectroluminescences, which emit light with three primary colors, areformed over the same substrate, the organic electroluminescences can bemanufactured in vacuum, in a reduced pressure space, or under a drynitrogen atmosphere without being exposed to atmospheric air throughoutall process (the patent document 4). However, Kuribayashi et al. alsodisclosed that a stacked body including a hole injecting layer, a lightemitting layer, and an Alq₃ layer is formed in vacuum or in a reducedpressure space without being exposed to atmospheric air, and then afterforming a counter electrode, treatment is performed under the drynitrogen atmosphere. However, in the patent document 4, it has not beendisclosed that after forming a mixed layer, the mixed layer is exposedto a nitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen, and then a subsequent stacked film is formed withoutexposing the mixed layer to a gas atmosphere including oxygen.

When after forming a mixed layer, the mixed layer is exposed to anitrogen gas atmosphere without being exposed to a gas atmosphereincluding oxygen and a subsequent stacked film is formed withoutexposing the mixed layer to a gas atmosphere including oxygen, life oflight emitting luminance can be improved without reducing productivityand deteriorating a characteristic of a light emitting device.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1D are cross sectional views explaining a method formanufacturing a light emitting device of the present invention;

FIGS. 2A and 2B are cross sectional views explaining a method formanufacturing a light emitting device of the present invention;

FIGS. 3A and 3B are cross sectional views explaining a method formanufacturing a light emitting device of the present invention;

FIG. 4 is a cross sectional view explaining a method for manufacturing alight emitting device of the present invention;

FIGS. 5A and 5B are cross sectional views explaining a method formanufacturing a light emitting device of the present invention;

FIGS. 6A and 6B are cross sectional views explaining a method formanufacturing a light emitting device of the present invention;

FIG. 7 is a diagram explaining a method for manufacturing a lightemitting device of the present invention;

FIGS. 8A and 8B are diagrams explaining a method for manufacturing alight emitting device of the present invention;

FIG. 9 is a diagram explaining an apparatus used for manufacturing alight emitting device of the present invention;

FIGS. 10A to 10E are cross sectional views explaining a method formanufacturing a light emitting device of the present invention;

FIGS. 11A to 11C are cross sectional views explaining a method formanufacturing a light emitting device of the present invention;

FIGS. 12A and 12B are cross sectional views explaining a light emittingdevice;

FIG. 13 is a diagram explaining a pixel portion of a light emittingdevice;

FIG. 14A is a top view and FIG. 14B is a cross sectional view explaininga light emitting device;

FIGS. 15A to 15F are diagrams explaining pixel circuits of a lightemitting device;

FIG. 16 is a diagram explaining a protection circuit of a pixel circuitof a light emitting device;

FIGS. 17A to 17E are diagrams explaining electronic appliances and thelike to which light emitting devices manufactured according to thepresent invention are applicable;

FIGS. 18A and 18B are diagrams explaining electronic appliances and thelike to which light emitting devices manufactured according to thepresent invention are applicable;

FIG. 19 is a cross sectional view explaining a method for manufacturinga light emitting device of the present invention;

FIG. 20 is a graph explaining reliability of light emitting devices 1and 2 of an embodiment;

FIG. 21 is a cross sectional view explaining a method for manufacturinga light emitting device of the present invention;

FIG. 22 is a cross sectional view explaining a method for manufacturinga light emitting device of the present invention; and

FIG. 23 is a cross sectional view explaining a method for manufacturinga light emitting device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Embodiment Modes

The embodiment modes of the present invention will be described belowwith reference to the accompanying drawings. It is easily understood bythose skilled in the art that the embodiment modes and details hereindisclosed can be modified in various ways without departing from thepurpose and the scope of the invention. The present invention should notbe interpreted as being limited to the description of the embodimentmodes to be given below.

Embodiment Mode 1

In a method for manufacturing a light emitting device including ananode, a cathode, a light emitting layer provided between the anode andthe cathode, and a mixed layer including an organic compound and metaloxide provided between the anode and the light emitting layer, thisembodiment mode will explain treatment in which the mixed layer isexposed to a nitrogen gas atmosphere after formation of the mixed layer.

An anode 2 is formed over a substrate 1 to have a thickness of 10 to1,000 nm (FIG. 1A). As the substrate 1, quartz, glass, plastic, or thelike can be used, for example. Further, other material may be used asthe substrate 1 so long as it can serve as a supporting body in aprocess of manufacturing the light emitting device.

The anode 2 has a function of injecting holes to the light emittinglayer. The anode 2 can be formed by using various kinds of metal; analloy; an electroconductive compound; or a metal mixture thereof. Forexample, metal having a conductive property such as aluminum (Al),silver (Ag), gold (Au), platinum (Pt), nickel (Ni), tungsten (W),chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu),palladium (Pd), lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca),strontium (Sr), and titanium (Ti); an alloy thereof such asaluminum-silicon (Al—Si), aluminum-titanium (Al—Ti), andaluminum-silicon-copper (Al—Si—Cu); nitride of a metal material such astitanium nitride (TiN); a metal compound such as ITO (indium tin oxide),ITO containing silicon oxide (ITSO), and IZO (indium zinc oxide) inwhich zinc oxide (ZnO) is mixed in indium oxide; or the like can beused.

The anode 2 is generally formed using a material having a high workfunction (e.g., 4.0 eV or more) so as to be able to inject holes. In thepresent invention, however, since a mixed layer 3 is formed on the anode2, the anode 2 is not limited to a material having a high work function,and a material having a low work function can be used.

After forming a film using the above mentioned material over thesubstrate 1 by sputtering or CVD, the film is subjected tophotolithography and etching to form the anode 2.

Prior to forming the mixed layer 3, heat treatment is performed here toremove moisture contained in the substrate 1 and the anode 2 (FIG. 1B).For example, the heat treatment can be carried out at 100 to 200° C.,e.g., 150° C., in vacuum or under reduced pressure. After this heattreatment, each layer is preferably formed in vacuum or under reducedpressure without being exposed to atmospheric air.

Next, the mixed layer 3 including an organic compound and metal oxide isformed in vacuum or under reduced pressure (FIG. 1C). This can preventshort-circuiting between the anode 2 and a cathode 7 due to concavityand convexity formed on the surface of the anode 2 or an extraneousmaterial left on the surface of each electrode. The thickness of themixed layer 3 is desirably 60 nm or more. More preferably, the thicknessof the mixed layer 3 is 120 nm or more. Even when the thickness of themixed layer 3 is increased, driving voltage of the light emitting deviceis not increased. Further, increasing the thickness of the mixed layerdoes not increase power consumption.

As the metal oxide, oxide or nitride of transition metal is desirable.Specifically, zirconium oxide, hafnium oxide, vanadium oxide, niobiumoxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide,titanium oxide, manganese oxide, or rhenium, oxide is preferable.

An the organic compound, an organic material having an arylamine groupsuch as 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation:NPB), 4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (abbreviation:TPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation:TDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis{N-[4-(N,N-di-m-tolylamino)phenyl]-N-phenylamino}biphenyl(abbreviation: DNTPD), 1,3,5-tris[N,N-di(m-tolyl)amino]benzene(abbreviation: m-MTDAB), or 4,4′,4″-tris(N-carbazolyl)triphenylamine(abbreviation: TCTA); phthalocyanine (abbreviation: H₂Pc); copperphthalocyanine (abbreviation: CuPc); vanadylphthalocyanine(abbreviation: VOPc); or the like can be used.

Further, an organic material represented by the following generalformula (1) can be preferably used. As specific examples of such anorganic material,3-[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2), and the like can be given. An organic compoundhaving the structure is superior in heat stability and has preferablereliability.

(In the general formula (1), R¹ and R³ may be may be identical to ordifferent from each other, and independently represent any of hydrogen,an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 25carbon atoms, a heteroaryl group having 5 to 9 carbon atoms, anarylalkyl group, and an acyl group having 1 to 7 carbon atoms. Ar¹represents either an aryl group having 6 to 25 carbon atoms or aheteroaryl group having 5 to 9 carbon atoms. R² represents any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, and an aryl grouphaving 6 to 12 carbon atoms. R⁴ represents any one of hydrogen, an alkylgroup having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbonatoms, and a substituent represented by the following general formula(2). In the substituent represented by the general formula (2), R⁵represents any one of hydrogen, an alkyl group having 1 to 6 carbonatoms, an aryl group having 6 to 25 carbon atoms, a heteroaryl grouphaving 5 to 9 carbon atoms, an arylalkyl group, and an acyl group having1 to 7 carbon atoms. Ar² represents either an aryl group having 6 to 25carbon atoms or a heteroaryl group having 5 to 9 carbon atoms. R⁶represents any one of hydrogen, an alkyl group having 1 to 6 carbonatoms, and an aryl group having 6 to 12 carbon atoms.)

As a method for synthesizing a carbazole derivative, various reactionsare applicable. For example, methods shown in the following reactionscheme (A-1) and reaction scheme (A-2) can be given. However, the methodfor synthesizing a carbazole derivative is not limited thereto.

Further, an organic material represented by any one of the followinggeneral formulas (3) to (6) can be preferably used. As specific examplesof an organic compound represented by any one of the following generalformulas (3) to (6), N-(2-naphthyl)carbazole (abbreviation: NCz);4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP);9,10-bis[4-(N-carbazolyl)phenyl]anthracene (abbreviation: BCPA);3,5-bis[4-(N-carbazolyl)phenyl]biphenyl (abbreviation: BCPBi);1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB); and thelike can be given.

In the general formula (3), Ar³ represents an aromatic hydrocarbon grouphaving 6 to 42 carbon atoms, n represents a natural number of 1 to 3,and R¹¹ and R¹² independently represent any of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, and an aryl group having 6 to 12 carbonatoms.

Note that in the general formula (4), Ar⁴ represents a univalentaromatic hydrocarbon group having 6 to 42 carbon atoms, and R²¹ and R²²independently represent any of hydrogen, an alkyl group having 1 to 4carbon atoms, and an aryl group having 6 to 12 carbon atoms.

Note that in the general formula (5), Ar⁵ represents a bivalent aromatichydrocarbon group having 6 to 42 carbon atoms, and R³¹ to R³⁴independently represent any one of hydrogen, an alkyl group having 1 to4 carbon atoms, and an aryl group having 6 to 12 carbon atoms.

Note that in the general formula (6), Ar⁶ represents a trivalentaromatic hydrocarbon group having 6 to 42 carbon atoms, and R⁴¹ to R⁴⁶independently represent any of hydrogen, an alkyl group having 1 to 4carbon atoms, and an aryl group having 6 to 12 carbon atoms.

Aromatic hydrocarbon such as anthracene, 9,10-diphenylanthracene(abbreviation: DPA), 2-tert-butyl-9,10-di(2-naphthyl)anthracene(abbreviation: t-BuDNA); tetracene, rubrene, and pentacene can be used.

A compound with large steric hindrance may be added to the mixed layer 3by co-evaporation or the like. This can prevent crystallization of themixed layer 3. As the compound with large steric hindrance (i.e., havinga structure with spatial spread, which is different from a planarstructure), 5,6,11,12-tetraphenyltetracene (abbreviation: rubrene) ispreferable. Note that in addition to that, hexaphenylbenzene,diphenylanthracene, t-butylperylene, 9,10-di(phenyl)anthracene, coumarin545T, or the like may be used. In addition, dendrimer, and the like canbe used.

The mixed layer 3 can be formed by co-evaporation of the above describedmetal oxide and organic compound. Further, it can also be formed by awet method, a droplet discharging method, or the like. Note that in acase of forming the mixed layer 3, it is necessary to prevent the mixedlayer from being exposed to a gas atmosphere including oxygen. When themixed layer 3 is formed by evaporation, a pattern is formed by providinga mask made from metal or the like between an evaporation source and thesubstrate. Note that in the mixed layer 3, a weight ratio between theorganic compound and the metal oxide is desirably set to be 95:5 to20:80, and more preferably, 90:10 to 50:50.

Next, the mixed layer 3 is exposed to a nitrogen gas atmosphere at aroom temperature without heating and without being exposed to a gasatmosphere including oxygen (FIG. 1D). In FIG. 1D, nitrogen (N₂) isschematically shown by circles. In FIG. 3B, FIGS. 5A and 5B, FIGS. 6Aand 6B, and FIG. 8B, nitrogen (N₂) is also schematically shown bycircles. Nitrogen gas is introduced in a chamber in which the substrate1 over which the mixed layer 3 is formed is set. Moisture is desirablyremoved from the nitrogen gas as much as possible, and the amount ofmoisture contained in the nitrogen gas is set to be 40 ppm or less, andpreferably, 3 ppm or less. The nitrogen gas is introduced in the chamberat a flow rate of 1 to 500 sccm such that pressure inside the chamberbecomes 1×10⁻¹ to 1×10⁶ Pa. While maintaining the pressure inside thechamber, the substrate 1 is left for 1 to 24 hours such that the mixedlayer 3 is exposed to the nitrogen gas atmosphere. Alternatively, themixed layer 3 may be sprayed with the nitrogen gas. In this case, thesubstrate 1 is not necessary to be left for 1 to 24 hours, and thenitrogen gas may be sprayed for 10 to 180 minutes. After the mixed layer3 is exposed to the nitrogen gas atmosphere, the nitrogen gas inside thechamber may be removed to made a vacuum state or a reduced pressurestate, and then the mixed layer 3 may be exposed to a nitrogen gasatmosphere again as described above. This can prolong the life of thelight emitting device.

Next, a hole transporting layer 4 is formed to have a thickness of 5 to50 nm in vacuum or under reduced pressure by evaporation or the likewithout exposing the mixed layer 3 to a gas atmosphere including oxygen(FIG. 2A). The hole transporting layer 4 is a layer having an excellenthole transporting property, for example, a layer formed using anaromatic amine (i.e., having a benzene ring-nitrogen bond) compound suchas NPB, TPD, TDATA, MTDATA, or BSPB. These substances mentioned heremainly have hole mobility of 1×10⁻⁶ to 10 cm²/Vs. Note that othersubstance may be used so long as it has a stronger hole transportingproperty than an electron transporting property. Note that the holetransporting layer 4 may be formed by not only a single layer but also astacked layer in which two or more layers made from the above mentionedsubstances are stacked.

Subsequently, a light emitting layer 5 is formed to have a thickness of5 to 10 nm in vacuum or under reduced pressure by evaporation or thelike (FIG. 2A). The light emitting layer 5 is not particularly limited.Layers serving as the light emitting layer are broadly classified intotwo modes. One mode is a host-guest type layer in which a light emittingsubstance (a dopant material), which becomes a light emitting center, isdispersed in a layer made from a material (a host material) with largerenergy gap than that of the light emitting substance. Another mode is alight emitting layer, which is formed only by using a light emittingmaterial. The former layer has preferable structure since lightquenching due to a concentration does not easily occur. As the lightemitting substance, which becomes the light emitting center,4-dicyanomethylene-2-methyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran(abbreviation: DOT);4-dicyanomethylene-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran;periflanthene;2,5-dicyano-1,4-bis(10-methoxy-1,1,7,7-tetramethyljulolidyl-9-enyl)benzene;N,N′-dimethylquinacridon (abbreviation: DMQd); coumarin 6; coumarin545T; tris(8-quinolinolato)aluminum (abbreviation: Alq₃);9,9′-bianthryl; 9,10-diphenylanthracene (abbreviation: DPA);9,10-bis(2-naphthyl)anthracene (abbreviation: DNA);2,5,8,11-tetra-t-butylperylene (abbreviation: TBP); and the like can begiven.

In addition, the following substances, which emit phosphorescence, canbe used as a dopant material:bis[2-(3,5-bis(trifluoromethyl)phenyl)pyridinato-N,C^(2′)]iridium(III)picolinato(abbreviation: Ir(CF₃ppy)₂(pic));bis[2-(4,6-difluorophenyl)pyridinato-N,C²′]iridium(III)acetylacetonato(abbreviation: FIr(acac));bis[2-(4,6-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)picolinato(abbreviation: FIr(pic)); tris(2-phenylpyridinato-N,C^(2′))iridium(abbreviation: Ir(ppy)₃); and the like.

As the host material, an anthracene derivative such as9,10-di(2-naphthyl)-2-tert-butylanthracene (abbreviation: t-BuDNA); acarbazole derivative such as 4,4′-bis(N-carbazolyl)biphenyl(abbreviation: CBP); a metal complex such astris(8-quinolinolato)aluminum (abbreviation: Alq₃),tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllinm (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum (abbreviation:BAlq), bis[2-(2-hydroxyphenyl)pyridinato]zinc (abbreviation: Znpp₂), orbis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: ZnBOX); or thelike can be used. Furthermore, as a material only by which the lightemitting layer 5 can be fainted, tris(8-quinolinolato)aluminum(abbreviation: Alq₃), 9,10-bis(2-naphthyl)anthracene (abbreviation:DNA), bis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum(abbreviation: BAlq), and the like can be given.

An electron transporting layer 6 is formed to have a thickness of 5 to100 nm over the light emitting layer 5 in vacuum or under reducedpressure by evaporation or the like (FIG. 2A). The electron transportinglayer 6 is a layer having an excellent electron transporting property,and for example, a layer formed using a metal complex having a quinolineskeleton or a benzoquinoline skeleton such astris(8-quinolinolato)aluminum (abbreviation: Alq₃),tris(5-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq₂), andbis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum (abbreviation:BAlq). In addition, a metal complex having an oxazole ligand or athiazole ligand such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc(abbreviation: ZnBOX) and bis[2-(2-hydroxyphenyl)benzothiazolato]zinc(abbreviation: Zn(BTZ)₂); and the like can be used. In addition to themetal complexes,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD); 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene(abbreviation: OXD-7);3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: TAZ);3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ); bathophenanthroline (abbreviation: BPhen);bathocuproin (abbreviation: BCP); and the like can be used. Thesesubstances mentioned here mainly have electron mobility of 1×10⁻⁶ to 10cm²/Vs. Note that other substance may be used as the electrontransporting layer 6 so long as it has a stronger electron transportingproperty than a hole transporting property. Further, the electrontransporting layer 6 may be formed by not only a single layer but also astacked layer in which two or more layers made from the above mentionedsubstances are stacked.

A cathode 7 is formed to have a thickness of 10 to 200 nm over theelectron transporting layer 6 in vacuum or under reduced pressure byevaporation or the like, and thus the light emitting device is completed(FIG. 2A). The cathode 7 can be formed by using metal having a low workfunction (3.8 eV or less), an alloy, an electroconductive compound, amixture thereof, or the like. As specific examples of a cathodematerial, an element belonging to Group 1 or 2 of the periodic table,i.e., alkali metal such as lithium (Li) or cesium (Cs), alkali earthmetal such as magnesium (Mg), calcium (Ca), or strontium (Sr), and analloy containing these substances (e.g., Mg:Ag, Al:Li, or the like) canbe given. However, when providing a layer having an excellent electroninjecting property (an electron injecting layer, not shown) is providedbetween the cathode 7 and the light emitting layer 5 to be in contactwith the cathode 7, the cathode 7 can be formed by using various kindsof conductive materials including the materials given for the materialsof the anode 2 such as Al, Ag, ITO, and ITO containing silicon,regardless of a work function.

Note that as the layer having the excellent electron injecting property,a compound of alkali metal or alkali earth metal such as lithiumfluoride (LiF), cesium fluoride (CsF), and calcium fluoride (CaF₂) canbe used. In addition, a substance having an electron transportingproperty, which contains alkali metal or alkali earth metal, and forexample, Alq₃ containing magnesium (Mg) or the like can be used.

The mixed layer 3, the hole transporting layer 4, the light emittinglayer 5, and the electron transporting layer 6 can be formed byevaporation. Alternatively, these layers can be formed by a dropletdischarging method or a wet method such as spin coating. Note that themixed layer 3 and layers stacked thereover are necessary to be formedwithout being exposed to a gas atmosphere including oxygen. Furthermore,a different method may be used to form each electrode or for each layer.

Since the light emitting device is sometimes deteriorated by moistureand the like, formation of a passivation film or sealing may be carriedout as described below.

In this embodiment mode, as a passivation film 8, a silicon oxide filmcontaining nitrogen is formed to have a thickness of 10 to 1,000 nm byplasma CVD, sputtering, or the like. When using the silicon oxide filmcontaining nitrogen, a silicon oxynitride film may be formed using SiH₄,N₂O, and NH₃ by plasma CVD; or a silicon oxynitride film may be formedusing SiH₄ and N₂O by plasma CVD; or a silicon oxynitride film may beformed using a gas in which SiH₄ and N₂O are diluted with Ar by plasmaCVD.

Further, a hydrogenated silicon oxynitride film formed using SiH₄, N₂O,and H₂ may be employed. Of course, the passivation film is not limitedto a single layer structure, and may include a single layer structure ora stacked layer structure including other insulating layer containingsilicon. Further, a multilayer film of a carbon nitride film and asilicon nitride film, a multilayer film of styrenepolymer, a siliconnitride film, or a diamond like carbon film may be formed as substitutefor the silicon oxide film containing nitrogen.

Subsequently, sealing is performed to protect the light emitting devicefrom a substance promoting deterioration such as moisture (FIG. 2B). Inthis embodiment mode, a counter substrate 11 is used for sealing, andthe counter substrate 11 is attached by a sealing material having aninsulating property such that an external connection portion is exposed.A space between the counter substrate 11 and the substrate 1 may befilled with an inert gas such as dry nitrogen. Alternatively, a sealingmaterial or a resin 9 having a light transmitting property may beapplied over a surface and the counter substrate 11 may be attached tothe substrate 1 by using it. An ultraviolet curing resin or the like ispreferably used as the sealing material. A drying agent 10 or particles10 for keep a constant gap between the substrates may be mixed in thesealing material. Subsequently, a flexible wiring substrate is attachedto the external connection portion. In this light emitting device, afterforming the mixed layer 3, the mixed layer is exposed to the nitrogengas atmosphere without being exposed to a gas atmosphere includingoxygen, and therefore, the life of the light emitting device can beprolonged.

As set forth above, the anode 2 is formed over the substrate 1 and themixed layer 3 is formed over the anode 2. Alternatively, this embodimentmode is applicable to a light emitting device having a structure inwhich the cathode 7 is formed over the substrate 1, the electrontransporting layer 6 is formed over the cathode 7, the light emittinglayer 5 is formed over the electron transporting layer 6, the holetransporting layer 4 is formed over the light emitting layer 5, themixed layer 3 is formed over the hole transporting layer 4, and theanode 2 is formed over the mixed layer 3 (FIG. 21).

After forming the mixed layer 3, the mixed layer 3 is exposed to thenitrogen gas atmosphere, where moisture is reduced as much as possible,at a room temperature without being exposed to a gas atmosphereincluding oxygen, and then the anode 2 is formed without exposing themixed layer 3 to a gas atmosphere including oxygen.

As a method for exposing the mixed layer 3 to the nitrogen gasatmosphere, the above described method can be employed. Further, afterthe mixed layer 3 is exposed to the nitrogen gas atmosphere, thenitrogen gas may be evacuated, and then the mixed layer 3 may be exposedto a nitrogen gas atmosphere again. Alternatively, the mixed layer 3 maybe sprayed with the nitrogen gas so as to be exposed to the nitrogen gasatmosphere.

In this case, the substrate 1, the cathode 7, the electron transportinglayer 6, the light emitting layer 5, the hole transporting layer 4, themixed layer 3, and the anode 2 described above can be used. Further, thelight emitting device can be manufactured in vacuum or under reducedpressure by evaporation or the like as described above.

Moreover, an electron injecting layer may be formed between the cathode7 and the electron transporting layer 6.

Embodiment Mode 2

In this embodiment mode, a structure different from the structure shownin Embodiment Mode 1 will be described. In the structure shown in thisembodiment mode, the mixed layer 3 is provided to be in contact with thecathode.

FIG. 3A shows one example of a structure of a light emitting device. InFIG. 3A, the hole transporting layer 4, the light emitting layer 5, theelectron transporting layer 6, a first layer 15, the mixed layer 3 arestacked between the anode 2 and the cathode 7. The anode 2, the cathode7, the hole transporting layer 4, the light emitting layer 5, theelectron transporting layer 6, and the mixed layer 3 shown in EmbodimentMode 1 can be used in this embodiment mode.

The first layer 15 is an electron injecting layer and contains asubstance having an electron donating property and a substance having anelectron transporting property. As the substance having the electrondonating property contained in the first layer 15, alkali metal, alkaliearth metal, or oxide or salt thereof is preferable. Specifically,lithium, cesium, calcium, lithium oxide, calcium oxide, barium oxide,cesium carbonate, and the like can be given. As the substance having theelectron transporting property, the compounds, which can be used forforming the electron transporting layer described in Embodiment Mode 1,can be used. The first layer 15 is formed to have a thickness of 1 to100 nm by evaporation or the like.

After forming the first layer 15, the mixed layer 3 is formed in vacuumor under reduced pressure as shown in Embodiment Mode 1. Thereafter, themixed layer 3 is exposed to a nitrogen gas atmosphere at a roomtemperature without being exposed to a gas atmosphere including oxygen(FIG. 3B). The amount of moisture contained in the nitrogen gas is setto be 40 ppm or less, and preferably, 3 ppm or less. The nitrogen gas isintroduced in a chamber, in which a substrate 1 over which the mixedlayer 3 is formed is set, at a flow rate of 1 to 500 scmm such thatpressure inside the chamber becomes 1×10⁻¹ to 1×10⁶ Pa.

While maintaining the pressure inside the chamber to be the abovedescribed pressure value, the substrate 1 is left for 1 to 24 hours sothat the mixed layer 3 is exposed to the nitrogen gas atmosphere.Alternatively, the mixed layer 3 may be sprayed with nitrogen gas. Inthis case, the substrate 1 is not necessary to be left for 1 to 24hours, and the nitrogen gas may be sprayed for 10 to 180 minutes.

After the mixed layer 3 is exposed to the nitrogen gas atmosphere, thenitrogen gas inside the chamber is removed to make a vacuum state or areduce pressure state, and then the mixed layer 3 may be exposed to anitrogen gas atmosphere again as described above. This can prolong thelife of the light emitting device.

Thereafter, the cathode 7 is formed in vacuum or under reduced pressurewithout exposing the mixed layer 3 to a gas atmosphere including oxygen,and thus the light emitting device is completed. Further, in the samemanner as Embodiment Mode 1, the passivation film 8 may be formed, andthen sealing may be performed to protect the light emitting device froma substance promoting deterioration such as moisture.

As set forth above, the anode 2 is formed over the substrate 1, and themixed layer 3 and the cathode 7 are formed over the anode 2. However,this embodiment mode is applicable to a light emitting device having astructure in which the cathode 7 is formed over the substrate 1, themixed layer 3 is formed over the cathode 7, the first layer 15 is formedover the mixed layer 3, the electron transporting layer 6 is formed overthe first layer 15, the light emitting layer 5 is formed over theelectron transporting layer 6, the hole transporting layer 4 is formedover the light emitting layer 5, and the anode 2 is formed over the holetransporting layer 4 (FIG. 22).

After forming the mixed layer 3, the mixed layer 3 is exposed to thenitrogen gas atmosphere, where moisture is reduced as much as possible,at a room temperature without exposing the mixed layer 3 to a gasatmosphere including oxygen, and then the first layer 15 is formedwithout exposing the mixed layer to a gas atmosphere including oxygen.

As a method for exposing the mixed layer 3 to the nitrogen gasatmosphere, the above described method can be employed. Further, afterthe mixed layer 3 is exposed to the nitrogen gas atmosphere, thenitrogen gas may be evacuated, and then the mixed layer 3 may be exposedto a nitrogen gas atmosphere again. Alternatively, the mixed layer 3 maybe sprayed with nitrogen gas so as to be exposed to the nitrogen gasatmosphere.

The substrate 1, the cathode 7, the mixed layer 3, the first layer 15,the electron transporting layer 6, the light emitting layer 5, the holetransporting layer 4, and the anode 2 as described above can be used inthis case. Further, the light emitting device can be manufactured invacuum or under reduced pressure by evaporation or the like as describedabove.

Moreover, a hole injecting layer may be formed between the holetransporting layer 4 and the anode 2.

Embodiment Mode 3

In this embodiment mode, mixed layers are provided to be in contact witha cathode and an anode.

An example of a structure of a light emitting device is shown in FIG. 4.In FIG. 4, a first mixed layer 3, a hole transporting layer 4, a lightemitting layer 5, an electron transporting layer 6, a first layer 15,and a second mixed layer 3 are stacked between an anode 2 and a cathode7. They can be formed by using the layers, the anode, and the cathodeshown in Embodiment modes 1 and 2. Further, an organic compound andmetal oxide used for the first mixed layer may be identical to ordifferent from an organic compound and metal oxide used for the secondmixed layer.

After forming the first mixed layer 3 and the second mixed layer 3 invacuum or under reduced pressure, the first and second mixed layers 3are exposed to a nitrogen gas atmosphere at a room temperature withoutbeing exposed to a gas atmosphere including oxygen as shown inEmbodiment Modes 1 and 2 (FIGS. 5A and 5B). The amount of moisturecontained in the nitrogen gas is set to be 40 ppm or less, andpreferably, 3 ppm or less. The nitrogen gas is introduced in thechamber, in which the substrate 1 over which the first and second mixedlayers 3 are formed is set. Moisture is desirably removed from thenitrogen gas as much as possible. The nitrogen gas is introduced at aflow rate of 1 to 500 sccm such that pressure inside the chamber becomes1×10⁻¹ to 1×10⁶ Pa.

While maintaining the pressure inside the chamber, the substrate 1 isleft for 1 to 24 hours so that the first and second mixed layers 3 areexposed to the nitrogen gas atmosphere. Alternatively, the first andsecond mixed layers 3 may be sprayed with the nitrogen gas. In thiscase, the substrate 1 is not necessary to be left for 1 to 24 hours, andthe nitrogen gas may be sprayed for 10 to 180 minutes.

After the first and second mixed layers 3 are exposed to the nitrogengas atmosphere, the nitrogen gas inside the chamber is removed to made avacuum state or a reduced pressure state, and then the first and secondmixed layers 3 are exposed to a nitrogen gas atmosphere again asdescribed above. Thereafter, the hole transporting layer 4 and thecathode 7 are fainted in vacuum or under reduced pressure withoutexposing the first and second mixed layers to a gas atmosphere includingoxygen. This can prolong the life of the light emitting device.

As set forth above, the anode 2 is formed over the substrate 1, and thecathode 7 is formed over the anode 2. However, this embodiment mode isapplicable to a light emitting device having a structure in which thecathode 7 is formed over the substrate 1, the first mixed layer 3 isformed over the cathode 7, the first layer 15 is formed over the firstmixed layer 3, the electron transporting layer 6 is formed over thefirst layer 15, the light emitting layer 5 is formed over the electrontransporting layer 6, the hole transporting layer 4 is formed over thelight emitting layer 5, the second mixed layer 3 is formed over the holetransporting layer 4, and the anode 2 is formed over the second mixedlayer 3 (FIG. 23).

After forming the first mixed layer 3, the first mixed layer 3 isexposed to the nitrogen gas atmosphere at a room temperature withoutbeing exposed to a gas atmosphere including oxygen, and then the firstlayer 15 is formed without exposing the first mixed layer 3 to a gasatmosphere including oxygen. Further, after forming the second mixedlayer 3, the second mixed layer 3 is exposed to the nitrogen gasatmosphere without being exposed to a gas atmosphere including oxygen,and then the anode 2 is formed without exposing the second mixed layer 3to a gas atmosphere including oxygen.

As a method for exposing the first and second mixed layers 3 to thenitrogen gas atmosphere, the above described method can be employed.Further, after the first and second mixed layers 3 are exposed to thenitrogen gas atmosphere, the nitrogen gas may be evacuated, and then thefirst and second mixed layers 3 may be exposed to a nitrogen gasatmosphere again. Alternatively, the first and second mixed layers 3 maybe sprayed with the nitrogen gas so as to be exposed to the nitrogen gasatmosphere. The amount of moisture contained in the nitrogen gas is setto be 40 ppm or less, and preferably, 3 ppm or less.

Moreover, the light emitting device can be formed in vacuum or underreduced pressure by evaporation or the like as described above.

Embodiment Mode 4

A mixed layer 3 is formed through a different method from the methodsshown in Embodiment Modes 1 to 3. In this embodiment mode, the mixedlayer 3 is not formed at once but formed in plural times.

As shown in FIGS. 1A and 1B, an anode 2 is formed over a substrate 1.The anode 2 is subjected to heat treatment in vacuum or under reducedpressure to remove moisture and the like. Then, a first mixed layer 17 ais formed to have a thickness of 10 to 30 nm in vacuum or under reducedpressure. Thereafter, the first mixed layer 17 a is exposed to anitrogen gas atmosphere where the moisture content is reduced as much aspossible, at a room temperature without being exposed to a gasatmosphere including oxygen as shown in the above embodiment modes (FIG.6A).

Next, a second mixed layer 17 b is formed to have a thickness of 10 to30 nm in vacuum or under reduced pressure while the first mixed layer 17a is not exposed to a gas atmosphere including oxygen. Thereafter, thesecond mixed layer 17 b is exposed to the nitrogen atmosphere where themoisture content is reduced as much as possible, at a room temperaturewithout being exposed to a gas atmosphere including oxygen in the samemanner as described in the above embodiment modes. Thus, a mixed layer 3is formed (FIG. 6B). While keeping constant pressure inside the chamber,the first and second mixed layers 17 a and 17 b are left for 1 to 24hours to be exposed to the nitrogen gas atmosphere as shown in the aboveembodiment modes. Alternatively, the first and second mixed layers 17 aand 17 b may be sprayed with the nitrogen gas.

Further, after the first and second mixed layers are exposed to thenitrogen gas atmosphere, the nitrogen gas in the chamber may be removedto form a vacuum state or a reduce pressure state, and then the firstand second mixed layers may be exposed to a nitrogen gas atmosphereagain.

Subsequently, a hole transporting layer and the like are formed invacuum or under reduced pressure without exposing the second mixed layer17 b to a gas atmosphere including oxygen so that the light emittingdevice is manufactured. This can prolong the life of the light emittingdevice.

This is applicable to a case where the mixed layer 3 is provided to bein contact with the cathode. Specifically, after forming the first layer(electron injecting layer) 15, the first mixed layer is formed, thefirst mixed layer is exposed to the nitrogen gas atmosphere, the secondmixed layer is formed, the second mixed layer is exposed to the nitrogengas atmosphere, and then the cathode is formed. Note that it is obviousthat this embodiment mode is applicable to the structures shown in theabove embodiment modes.

Further, this embodiment mode is applicable to a light emitting device,in which an anode 2 is formed over a substrate 1, an hole transportinglayer is formed over the anode 2, a light emitting layer is formed overthe hole transporting layer, an electron transporting layer is formedover the light emitting layer, a first layer is formed over the electrontransporting layer, a first mixed layer 3 is formed over the firstlayer, the first mixed layer is exposed to a nitrogen gas atmosphere ata room temperature, a second mixed layer is formed, the second mixedlayer is exposed to a nitrogen gas atmosphere where the moisture contentis reduced as much as possible, and then a cathode 7 is formed.

Furthermore, this embodiment mode is also applicable to a light emittingdevice, in which the cathode 7 is formed over a substrate 1, the firstmixed layer 3 layer is formed over the cathode 7, the first mixed layer3 is exposed to a nitrogen gas atmosphere at a room temperature, thesecond mixed layer is formed, the second mixed layer is exposed to thenitrogen gas atmosphere, the first layer 15 is formed, the electrontransporting layer 6 is formed over the first layer 15, the lightemitting layer 5 is formed over the electron transporting layer 6, thehole transporting layer 4 is formed over the light emitting layer 5, andthe anode 2 is formed over the hole transporting layer 4.

Moreover, this embodiment mode is also applicable to a light emittingdevice, in which the cathode 7 is formed over a substrate 1, theelectron transporting layer 6 is formed over the cathode 7, the lightemitting layer 5 is formed over the electron transporting layer 6, thehole transporting layer 4 is formed over the light emitting layer 5, thefirst mixed layer 3 layer is formed over the hole transporting layer 4,the first mixed layer 3 is exposed to a nitrogen gas atmosphere at aroom temperature, a second mixed layer is formed, the second mixed layeris exposed to the nitrogen gas atmosphere where the moisture content isreduced as much as possible, and the anode 2 is formed.

Embodiment Mode 5

In this embodiment mode, a structure different from the structures shownin the above embodiment modes will be described. Specifically, a lightemitting device (a tandem light emitting device) in which a plurality oflight emitting units are stacked, will be described. The light emittingdevice includes a plurality of light emitting units between an anode anda cathode. FIG. 7 shows a tandem light emitting device in which twolight emitting units are stacked. The plurality of light emitting unitsare connected in series through a charge generating layer, and a mixedlayer including an organic compound and metal oxide is applied to thecharge generating layer.

In FIG. 7, a first light emitting unit 22 and a second light emittingunit 24 are stacked between an anode 20 and a cathode 21. A chargegenerating layer 23 is formed between the first light emitting unit 22and the second light emitting unit 24.

The anode 20 and the cathode 21 can be respectively formed using thematerials shown in the above embodiment mode.

Each of the first light emitting unit 22 and the second light emittingunit 24 has a structure in which hole transporting layers, lightemitting layers, and electron transporting layers are stacked over theanode 20. Specifically, a whole of the first and second light emittingunits has a stacked structure in which an anode, a hole transportinglayer, a light emitting layer, an electron transporting layer, a chargegenerating layer, another hole transporting layer, another lightemitting layer, another electron transporting layer, and a cathode arestacked. The hole transporting layers and the electron transportinglayers are not necessarily provided in this structure, and may beprovided, if required. Further, a hole injecting layer, an electroninjecting layer, and the like may be provided, if required. The lightemitting units can be formed by using the materials show in the aboveembodiment mode.

The charge generating layer 23 is formed by combining a mixed layerincluding an organic compound and metal oxide shown in the aboveembodiment mode and a layer including a substance having an electrondonating property and a substance having an electron transportingproperty shown in the above embodiment mode. The charge generating layer23 may be formed by combining a mixed layer and a transparent conductivefilm. Since the mixed layer has high transmittance of visible light,transmittance of light generated in the first light emitting unit andthe second light emitting unit is also high, making it possible toimprove light extraction efficiency to an external portion.

As the substance having the electron donating property, alkali metal,alkali earth metal, or oxide or salt thereof is preferable.Specifically, lithium, cesium, calcium, lithium oxide, calcium oxide,barium oxide, cesium carbonate, and the like can be given. As thesubstance having the electron transporting property, the substances,which can be used for forming the electron transporting layer, can beused.

The anode 20 and the first light emitting unit 22 are formed over asubstrate, and then a layer 25 including the substance having anelectron donating property and a substance having an electrontransporting property is formed in vacuum or under reduced pressure byevaporation or the like. Next, a mixed layer 26 including an organiccompound and metal oxide is formed in vacuum or under reduced pressureby co-evaporation or the like (FIG. 8A).

Subsequently, the mixed layer 26 is exposed to a nitrogen gasatmosphere, where the moisture content is reduced as much as possible,at a room temperature by the method shown in the above embodiment modeswithout being exposed to a gas atmosphere including oxygen (FIG. 8B).This can improve life of the light emitting device.

Next, the second light emitting unit 24 is formed in vacuum or underreduced pressure without exposing the mixed layer 26 to a gas atmosphereincluding oxygen, and then the cathode 21 is formed. Thus, the lightemitting device as shown in FIG. 7 is completed. Note that sealing canbe performed by using the method described in the above embodiment mode.

Further, the mixed layer 26 can be formed by plural times as describedin Embodiment Mode 4.

A light emitting device having the two light emitting units is describedin this embodiment mode. Further, a light emitting element in whichthree or more light emitting units are stacked may also be formed byusing the materials shown in the present invention. For example, a lightemitting device having three light emitting units has a structure inwhich a first light emitting unit, a first charge generating layer, asecond light emitting unit, a second charge generating layer, and athird light emitting unit are stacked in this order. A mixed layerincluding an organic compound and metal oxide may only be contained inany one of the charge generating layers. Alternatively, mixed layerseach including an organic compound and metal oxide may be contained inall of the charge generating layers. Note that this embodiment mode canbe appropriately combined with other embodiment modes.

Each of the first light emitting unit 22 and the second light emittingunit 24 may have a structure in which an electron transporting layer, alight emitting layer, a hole transporting layer are stacked over acathode.

Further, this embodiment mode is applicable to a light emitting devicein which a cathode is formed, a first light emitting unit having a lightemitting layer is formed over the cathode, a mixed layer including anorganic compound and metal oxide is formed over the first light emittingunit, the mixed layer is exposed to a nitrogen gas atmosphere where themoisture content is reduced as much as possible at a room temperaturewithout being exposed to a gas atmosphere including oxygen, a layerincluding a substance having an electron donating property and asubstance having an electron transporting property is formed withoutexposing the mixed layer to a gas atmosphere including oxygen, a secondlight emitting unit is formed over the layer including the substancehaving the electron donating property and the substance having theelectron transporting property, and an anode is formed over the secondlight emitting unit.

Embodiment Mode 6

In this embodiment mode, an example of a process of manufacturing alight emitting device disclosed in the present invention and amulti-chamber manufacturing apparatus used in this process will bedescribed. In this embodiment mode, after a substrate is loaded into themulti-chamber manufacturing apparatus, films such as a mixed layer and alight emitting layer are successively formed, and then, the substrate isattached to a counter substrate, which is separately loaded into themulti-chamber manufacturing apparatus, so as to perform sealingtreatment.

An apparatus for manufacturing a light emitting device shown in FIG. 9has a delivery chamber 101 (attached with a delivery robot 111 fordelivering a substrate, a counter substrate, a metal mask, and thelike), a substrate/mask stock chamber 102 connected to the deliverychamber through a gate valve, a pretreatment chamber 103 connected tothe delivery chamber through a gate valve, a first evaporation chamber104 connected to the delivery chamber through a gate valve, a secondevaporation chamber 105 connected to the delivery chamber through a gatevalve, a third evaporation chamber 106 connected to the delivery chamberthrough a gate valve, a fourth evaporation chamber 110 connected to thedelivery chamber through a gate valve, a CVD chamber 107 connected tothe delivery chamber through a gate valve, a sealing glass stock chamber108 connected to the delivery chamber through a gate valve, and asealing chamber 109 connected to the delivery chamber through a gatevalve.

First, a substrate and an evaporation metal mask are loaded into thesubstrate/mask stock chamber 102. The substrate/mask stock chamber 102is made to load and unload the substrate to/from a chamber.

The substrate/mask stock chamber has an elevator structure, andsubstrates or masks share each stage of the elevator structure. A totalof up to 10 to 15 pieces of substrates and masks can be stored in thesubstrate/mask stock chamber. Note that an anode is formed over eachsubstrate outside the substrate/mask stock chamber.

On the other hand, a counter substrate is loaded in the sealing glassstock chamber 108. The sealing glass stock chamber has an elevatorstructure, in which a counter substrate, which is already subjected topretreatment (typically, which indicates attachment of a drying agentfor absorbing moisture inside and outside of a panel and formation of asealing material for attaching the counter substrate to the substrate)is stored in each stage.

In this manufacturing apparatus, films are formed over all of loadedsubstrates first. This is called an “evaporation mode”. Afterterminating the evaporation mode, a “sealing mode” for attaching thesubstrates to counter substrates starts.

The evaporation mode will be described below. First, the deliverychamber 101, the pretreatment chamber 103, the first evaporation chamber104, the second evaporation chamber 105, the third evaporation chamber106, the fourth evaporation chamber 110, and the CVD chamber 107 areevacuated to be a high vacuum state of 1×10⁻⁵ to 1×10⁻⁶ Pa. In theevaporation mode, the delivery chamber is always maintained in highvacuum. Further, each evaporation material set in each evaporationchamber is previously heated at a low temperature of 30° C. or less,which is lower than an evaporation starting temperature of eachmaterial. The pre-heating time is preferably set to be 12 hours or more.The pre-heating is performed to remove moisture attached to eachevaporation material.

Next, after vacuum evacuation of the substrate/mask stock chamber 102,masks are delivered to each evaporation chamber. After completion of theabove described preparation, a substrate is delivered to thepretreatment chamber 103. In the pretreatment chamber 103, the substrateis heated in vacuum or under reduced pressure by a lamp heater or thelike. Note that the substrate may be heated in the substrate/mask stockchamber 102.

Subsequently, the substrate is transported to the fourth evaporationchamber 110 through the delivery chamber 101 from the pretreatmentchamber 103. After termination of alignment treatment using a mask and aCCD camera, a mixed layer is formed over the substrate. In the fourthevaporation chamber 110, an organic compound and metal oxide areevaporated from fixed evaporation sources to form the mixed layer on thesubstrate, which is set over the evaporation sources. During theevaporation, the substrate is rotated. This improves distribution of athickness of the mixed film formed over the substrate.

Then, the substrate is delivered to the CVD chamber 107 through thedelivery chamber 101 while the substrate is not exposed to a gasatmosphere including oxygen. The CVD chamber 107 is evacuated to be ahigh vacuum state until the substrate is delivered to the CVD chamber107. After the delivery of the substrate, 1 to 500 sccm of high-puritynitrogen gas, in which the moisture content is reduced as much aspossible, is supplied to the CVD chamber. When the CVD chamber isevacuated by a turbo booster pump during a period of supplying thenitrogen gas, pressure inside the CVD chamber is constant. The pressureis preferably 1×10⁻¹ to 1×10⁶ Pa. After the nitrogen gas is sprayed tothe substrate for 10 to 180 minutes and the substrate is exposed to thenitrogen gas, the supply of the nitrogen gas is stopped.

Alternatively, after the nitrogen gas is evacuated to made the CVDchamber in a high vacuum state, the nitrogen gas may be supplied to theCVD chamber again so that the substrate may be exposed to the nitrogengas. Further, in a case where the substrate is not sprayed with thenitrogen gas, the nitrogen gas is supplied to the CVD chamber whilekeeping the above mentioned pressure so that the substrate may beexposed to a nitrogen gas atmosphere for 1 to 24 hours.

Note that in the CVD chamber 107, a CVD film can be formed over anentire surface of the substrate. Further, plasma treatment can beperformed by using plural kinds of gases. By utilizing the plasmatreatment, for example, a protection film such as a silicon nitride filmor a silicon oxide film can be formed over a cathode. Furthermore, aspretreatment to the substrate, plasma treatment using plural kinds ofgases (for example, Ar+O₂ plasma treatment) may be performed.

Next, the substrate is delivered to the second evaporation chamber 105through the delivery chamber 101 without exposing the mixed layer to agas atmosphere including oxygen. After termination of alignmenttreatment, a hole transporting layer is formed.

Then, the substrate is delivered to the first evaporation chamber 104through the delivery chamber 101. A mechanism and a film formationmethod of the first evaporation chamber is the same as the otherevaporation chambers. In the first evaporation chamber 104, a lightemitting layer is formed, and then an electron transporting layer isformed. The light emitting layer may be formed by co-evaporation of ahost material and a dopant material. The switching of the formation ofthe electron transporting layer from the formation of the light emittinglayer is smoothly carried out only by closing an evaporation sourceshutter attached to each evaporation source.

Next, the substrate is delivered to the third evaporation chamber 106through the delivery chamber 101. In the third evaporation chamber 106,a cathode is formed. A mechanism and a film formation method of thethird evaporation chamber is the same as the other evaporation chambers.

The substrate subjected to necessary treatment as described above iscarried back to the substrate/mask stock chamber 102, which is astarting point, again through the delivery chamber 101. A series oftreatment required for obtaining a panel, which emits light with asingle color, is shown in this embodiment mode; however, the presentinvention is not limited thereto.

After termination of the same treatment with respect to all of loadedsubstrates and masks are collected to the substrate/mask stock chamber102 from each evaporation chamber, the evaporation mode is terminated,and then a sealing mode starts successively in this manufacturingapparatus.

The sealing mode will be described below. First, the delivery chamber101, the substrate/mask stock chamber 102, and the sealing glass stockchamber 108 are pressurized with nitrogen gas to have atmosphericpressure. This treatment may be performed to the delivery chamber andthe substrate/mask stock chamber immediately after the termination ofthe evaporation mode. Further, with respect to the sealing glass stockchamber, when a counter substrate, which is subjected to thepretreatment, is set immediately before sealing as much as possible,deterioration of a sealing material and a drying material can beinhibited. After setting the counter substrate, a concentration ofmoisture of the delivery chamber in a sealing mode can be reduced byperforming plural times of pressurizing treatment to the sealing glassstock chamber by evacuation of the sealing glass stock chamber andpressurization treatment with nitrogen gas. Further, defoaming of thesealing material formed over the counter substrate can be performed.

Next, the substrate is delivered to the sealing chamber 109 from thesubstrate/mask stock chamber 102 through the delivery chamber 101whereas the counter substrate is delivered to the sealing chamber 109from the sealing glass stock chamber 108 through the delivery chamber101. In the sealing chamber, after terminating alignment treatment ofthe substrate and the counter substrate such that the edge portions ofthe substrate and the counter substrate are adjusted, the substrate andthe counter substrate are attached to each other and pressurized toperform sealing. Further, ultraviolet ray irradiation is performed fromthe side (lower side) of the counter substrate to cure the sealingmaterial (which is a ultraviolet curing resin here). At this moment, byusing a light shielding mask, only a portion of the sealing material canbe selectively irradiated with ultraviolet ray.

Through the above described sealing treatment, the substrate and thecounter substrate becomes one panel. This panel is delivered to thesubstrate/mask stock chamber 102 from the sealing chamber 109 throughthe delivery chamber 101. Subsequently, other substrates and othercounter substrates are subjected to the same treatment. Panels areultimately stocked in the substrate/mask stock chamber, and then thesealing mode is terminated. After the termination of the sealing mode,the completed panels may be taken out from the substrate/mask stockchamber.

Embodiment Mode 7

In this embodiment mode, a light emitting device of the presentinvention will be described while showing a method for manufacturing thelight emitting device with reference to FIGS. 10A to 10E and FIGS. 11Ato 11C. Note that an example of manufacturing an active matrix lightemitting device will be described in this embodiment mode.

First, a first base insulating layer 51 a and a second base insulatinglayer 51 b are formed over a substrate 50, and then, a semiconductorlayer is formed over the second base insulating layer 51 b (FIG. 10A).

As the substrate 50, glass, quartz, plastic (such as polyimide, acrylic,polyethyleneterephthalate, polycarbonate, polyacrylate, andpolyethersulfone), and the like can be used. A substrate made from sucha material can be polished by CMP or the like, if required. In thisembodiment mode, a glass substrate is used.

The first base insulating layer 51 a and the second base insulatinglayer 51 b are provided to prevent an element such as alkali metal andalkali earth metal, which adversely affects a characteristic of thesemiconductor layer from dispersing in the semiconductor layer. Asmaterials of the first and second base insulating layers, silicon oxide,silicon nitride, silicon oxide containing nitrogen, silicon nitridecontaining oxygen, and the like can be used. In this embodiment mode,the first base insulating layer 51 a is formed using silicon nitride andthe second base insulating layer 51 b is formed using silicon oxide. Abase insulating film including two layers of the first base insulatinglayer 51 a and the second base insulating layer 51 b is provided in thisembodiment mode. Alternatively, a base insulating film including asingle layer or two or more layers may be provided. Further, ifdispersion of an impurity penetrating from the substrate causes noproblems, the base insulating layers are not necessary to be provided.

In this embodiment mode, the semiconductor layer formed after the firstand second base insulating layers are obtained by crystallizing anamorphous silicon film by laser beam. The amorphous silicon film isformed over the second base insulating layer 51 b to have a thickness of25 to 100 nm (preferably, 30 to 60 nm). As a method for forming theamorphous silicon film, a known method such as sputtering, reducedpressure CVD, and plasma CVD, can be used. Thereafter, heat treatment isperformed at 500° C. for one hour to perform dehydrogenation.

Subsequently, the amorphous silicon film is crystallized by using alaser irradiation apparatus to form a crystalline silicon film. In thisembodiment mode, an excimer laser is used in laser crystallization.Laser beam oscillated from the laser irradiation apparatus is processedinto a linear beam spot by using an optical system. The amorphoussilicon film is crystallized by being irradiated with the linear beamspot. The thus obtained crystalline silicon film is used as thesemiconductor layer.

As other method for crystallizing an amorphous silicon film, there are amethod by which crystallization is performed only by heat treatment, anda method by which crystallization is performed by heat treatment withuse of a catalytic element promoting crystallization. As an elementpromoting crystallization, nickel, iron, palladium, tin, lead, cobalt,platinum, copper, gold, and the like can be given. When using such anelement promoting crystallization, the crystallization can be carriedout at a lower temperature and a shorter time as compared to a case ofperforming crystallization only by heat treatment. Therefore, the glasssubstrate and the like are less damaged by the crystallization. Whencrystallization is performed only by heat treatment, a quartz substrate,which is resistant to heat, may be used as the substrate 50.

Subsequently, a minute amount of impurity is doped in the semiconductorlayer so as to control a threshold value, or, channel doping isperformed, if required. To obtain a required threshold value, animpurity (such as phosphorus and boron) imparting an N-type conductivityor a P-type conductivity is doped in the semiconductor layer by iondoping or the like.

Thereafter, as shown in FIG. 10A, the semiconductor layer is patternedinto a predetermined shape to obtain an island-like semiconductor layer52. This patterning is performed in such a way that a photoresist isformed over the semiconductor layer, a predetermined mask shape isexposed and baked to form a resist mask over the semiconductor layer,and the semiconductor layer is etched by utilizing the resist mask.

Subsequently, a gate insulating layer 53 is formed to cover thesemiconductor layer 52. The gate insulating layer 53 is formed using aninsulating layer containing silicon by plasma CVD or sputtering so as tohave a thickness of 40 to 150 nm. In this embodiment mode, silicon oxideis used to form the gate insulating layer 53.

Next, a gate electrode 54 is formed over the gate insulating layer 53.The gate electrode 54 may be formed by using an element selected fromtantalum, tungsten, titanium, molybdenum, aluminum, copper, chromium,and niobium; or an alloy material or a compound material mainlycontaining these elements. Further, a semiconductor film typified by apolycrystalline silicon film doped with an impurity element such asphosphorus may be used. Furthermore, an AgPdCu alloy may be used.

In this embodiment mode, the gate electrode 54 is formed to have asingle layer. Alternatively, the gate electrode 54 may have a stackedstructure including two or more layers, for example, a lower layer madefrom tungsten and an upper layer made from molybdenum. In a case wherethe gate electrode is formed to have a stacked structure, the abovementioned materials may be used. Further, a combination of thesematerials may be arbitrarily selected. The gate electrode 54 is etchedby utilizing a mask made from a photoresist.

Subsequently, a high concentration impurity is doped into thesemiconductor layer 52 while utilizing the gate electrode 54 as a mask.Thus, a thin film transistor 70 including the semiconductor layer 52,the gate insulating layer 53, and the gate electrode 54, is formed. Inthis case, an LDD region 57 may be provided by using low-speed iondoping or high-speed ion doping in addition to a source region 55 and adrain region 56.

Note that processes of manufacturing the thin film transistor are notparticularly limited, and may be arbitrarily changed so as tomanufacture a transistor having a desired structure.

In this embodiment mode, a top-gate thin film transistor using thecrystalline silicon film, which is crystallized by lasercrystallization, is used. Alternatively, a bottom-gate thin filmtransistor using an amorphous semiconductor film can be used. Theamorphous semiconductor film can be formed by using not only silicon butalso silicon germanium. When using silicon germanium, a concentration ofgermanium is preferably set to be about 0.01 to 4.5 atomic %.

Further, a microcrystalline semiconductor film (semiamorphoussemiconductor) in which 0.5 to 20 nm crystal grains can be observed inan amorphous semiconductor, may be used. Fine crystals, in which 0.5 to20 nm crystal grains can be observed, are also referred to asmicrocrystals (μc).

Semiamorphous silicon (also referred to as SAS), which is asemiamorphous semiconductor, can be obtained by glow dischargedecomposition of silane-based gas. As typical silane-based gas, SiH₄ canbe given, and in addition, Si₂H₆, SiH₂Cl₂, SiHCl₃, SiCl₄, SiF₄ and thelike can be used. By diluting such silane-based gas with hydrogen or amixture of hydrogen and one or more rare gas elements selected fromhelium, argon, krypton, and neon, the SAS can be formed easily. Thedilution ratio of the silane-based gas is preferably set to be in therange of 1:10 to 1:1,000. The semiamorphous silicon may be formed byglow discharge decomposition at the pressure of about 0.1 to 133 Pa. Thehigh-frequency power for glow discharge is preferably set to be 1 to 120MHz, and more preferably, 13 to 60 MHz. A substrate heating temperaturemay be set to be 300° C. or less, and preferably, 100 to 250° C.

Raman spectrum of the thus formed SAS is shifted toward lowerwavenumbers than 520 cm⁻¹. The diffraction peaks of (111) and (220),which are believed to be derived from Si crystal lattice, are observedin the SAS by X-ray diffraction. The semiamorphous semiconductorcontains hydrogen or halogen of at least 1 atomic % or more to terminatedangling bonds. With respect to impurity elements contained in the film,each concentration of impurities for atmospheric constituents such asoxygen, nitrogen, and carbon is preferably set to be 1×10²⁰ cm⁻³ orless. In particular, the oxygen concentration is set to be 5×10¹⁹ cm⁻³or less, and preferably, 1×10¹⁹ cm⁻³ or less.

Moreover, the SAS may be further crystallized by laser irradiation.

Subsequently, an insulating film (hydrogenated film) 59 is formed byusing silicon nitride so as to cover the gate electrode 54 and the gateinsulating layer 53. The insulating film (hydrogenated film) 59 isheated at 480° C. for about 1 hour to activate the impurity element andhydrogenate the semiconductor layer 52.

A first interlayer insulating layer 60 is formed to cover the insulatingfilm (hydrogenated film) 59. As a material for forming the firstinterlayer insulating layer 60, silicon oxide, acrylic, polyimide,siloxane, a low dielectric constant material, and the like may be used.In this embodiment mode, a silicon oxide film is formed as the firstinterlayer insulating layer (FIG. 10B).

Next, contact holes that reach the semiconductor layer 52 are formed.The contact holes can be formed using a resist mask by etching to exposethe semiconductor layer 52 through the contact holes. The contact holescan be formed by either wet etching or dry etching. Further, they may beformed by etching one or more times depending on a condition. Whenetching is performed plural times, both wet etching and dry etching maybe used (FIG. 10C).

A conductive layer is formed to cover the contact holes and the firstinterlayer insulating layer 60. This conductive layer is processed intoa desired shape to form a connection portion 61 a, a wiring 61 b, andthe like. This wiring may have a single layer made from aluminum,copper, an aluminum-carbon-nickel alloy, an aluminum-carbon-molybdenumalloy, or the like. Further, the wiring may have a structure formed bystacking molybdenum, aluminum, and molybdenum from the side of asubstrate, a structure formed by stacking titanium, aluminum, andtitanium from the side of a substrate, or a structure formed by stackingtitanium, titanium nitride, aluminum, and titanium from the side of asubstrate (FIG. 10D).

Thereafter, a second interlayer insulating layer 63 is formed to coverthe connection portion 61 a, the wiring 61 b, and the first interlayerinsulating layer 60. As a material of the second interlayer insulatinglayer 63, a film having a self-planarizing property such as acrylic,polyimide, and siloxane is preferably used. In this embodiment mode,siloxane is used to form the second interlayer insulating layer 63 (FIG.10E).

Subsequently, an insulating layer may be formed using silicon nitride orthe like over the second interlayer insulating layer 63 (not shown).This insulating layer is formed to prevent the second interlayerinsulating layer 63 from being etched more than necessary in etching apixel electrode that will be formed later. Therefore, when a ratio ofthe etching rates between the pixel electrode and the second interlayerinsulating layer 63 is large, this insulating layer may not be provided.Next, a contact hole is formed through the second interlayer insulatinglayer 63 to reach the connection portion 61 a.

A conductive layer having a light transmitting property is formed tocover the contact hole and the second interlayer insulating layer 63 (orthe insulating layer). Thereafter, the conductive layer having the lighttransmitting property is processed to form an anode 64. The anode 64 iselectrically connected to the connection portion 61 a here.

The anode 64 can be formed by using a conductive film shown inEmbodiment Mode 1, for example, metal having a conducting property suchas aluminum (Al), silver (Ag), gold (Au), platinum (Pt), nickel (Ni),tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co),copper (Cu), palladium (Pd), lithium (Li), cesium (Cs), magnesium (Mg),calcium (Ca), strontium (Sr), and titanium (Ti); an alloy thereof suchas aluminum-silicon (Al—Si), aluminum-titanium (Al—Ti), andaluminum-silicon-copper (Al—Si—Cu); nitride of a metal material such astitanium nitride (TiN); a metal compound such as ITO, ITO containingsilicon oxide (ITSO), and IZO.

Further, an electrode through which light is extracted may be formedusing a conductive film having a light transmitting property. Anextremely thin film of metal such as Al and Ag is used, in addition to ametal compound such as ITO, ITSO, or IZO. Furthermore, in a case wherelight is extracted through a cathode, the anode can be formed using amaterial having high reflectance (e.g., Al, Ag, or the like). In thisembodiment mode, the anode 64 is formed by using ITSO (FIG. 11A).

Next, an insulating layer is formed using an organic material or aninorganic material to cover the second interlayer insulating layer 63(or the insulating layer) and the anode 64. Subsequently, the insulatinglayer is processed to expose a part of the anode 64 so as to form apartition wall 65. A photosensitive organic material (such as acrylicand polyimide) is preferably used as a material of the partition wall65. In addition, the partition wall may be formed using anonphotosensitive organic or inorganic material. Further, a blackpigment such as titanium black and carbon nitride or a dye may bedispersed in a material of the partition wall 65 by using a dispersantso that the partition wall 65 may be used as a black matrix. Preferably,an edge of the partition wall 65, where faces the anode, has a tapershape such that the curvature is continuously varied (FIG. 11B).Thereafter, the substrate is heated in vacuum or under reduced pressureto remove moisture and the like.

Subsequently, a mixed layer including an organic compound and metaloxide is formed in vacuum or under reduced pressure to cover the anode64 exposed from the partition wall 65. This mixed layer has a structuredescribed in Embodiment Mode 1. In this embodiment mode, DNTPD is usedas the organic compound whereas molybdenum trioxide is used as the metaloxide. The mixed layer is formed by co-evaporation such that a weightratio of molybdenum trioxide to DNTPD is 10 to 80 wt %. Of course, themixed layer may be formed by using other materials described inEmbodiment Mode 1.

Thereafter, the mixed layer is exposed to a nitrogen gas atmosphere at aroom temperature without being exposed to a gas atmosphere includingoxygen in accordance with the method shown in the above embodimentmodes. Nitrogen gas is introduced into a chamber in which the substrateis set. Moisture is desirably removed as much as possible from thenitrogen gas in the same manner as the above embodiment modes.

Subsequently, a layer having an excellent hole transporting property, alight emitting layer, and an electron transporting layer are formed invacuum or under reduced pressure without exposing the mixed layer to agas atmosphere including oxygen. The layer having the excellent holetransporting property is formed using NPB by evaporation to have athickness of 10 to 100 nm. The light emitting layer is formed byco-evaporation of Alq₃ and coumarin 6 to have a thickness of 35 to 100nm such that a weight ratio between Alq₃ and coumarin 6 is set to be1:0.005. The electron transporting layer is formed using Alq₃ byevaporation to have a thickness of 10 to 100 nm. Accordingly, a lightemitting stacked body 66 including the mixed layer, the holetransporting layer, the light emitting layer, and the electrontransporting layer is formed over the anode 64.

A cathode 67 is next formed to cover the light emitting stacked body 66(FIG. 11C). A light emitting device 93 in which an organic layerincluding the light emitting layer is interposed between the anode 64and the cathode 67 can be manufactured. By applying higher voltage tothe anode 64 than the cathode 67, light emission can be obtained. As anelectrode material used for forming the cathode 67, the same materialused for forming the anode can be used. In this embodiment mode, thecathode is formed using aluminum. Thus, a light emitting device iscompleted.

Afterwards, a silicon oxide film containing nitrogen is formed as apassivation film by plasma CVD. When using a silicon oxide filmcontaining nitrogen, a silicon oxynitride film may be Mimed using SiH₄,N₂O, and NH₃ by plasma CVD, or a silicon oxynitride film may be formedusing SiH₄ and N₂O by plasma CVD, or a silicon oxynitride film may beformed using a gas in which SiH₄ and N₂O are diluted with Ar, by plasmaCVD.

Alternatively, as the passivation film, a hydrogenated siliconoxynitride film formed using SiH₄, N₂O, and H₂ by plasma CVD may beused. The passivation film is, of course, not limited to a single layerstructure, and it may have a single layer structure or a stackedstructure of other insulating layer containing silicon. In addition, amultilayer film including a carbon nitride film and a silicon nitridefilm, a multilayer film including styrene polymer, a silicon nitridefilm, or a diamond like carbon film may be formed instead of the siliconoxide film containing nitrogen.

Subsequently, to protect the light emitting device from a substancewhich promotes deterioration of the light emitting device such asmoisture, a display portion is sealed. When the display portion issealed with a counter substrate, the counter substrate is attached tothe display portion with an insulating sealing material such that anexternal connection portion is exposed. A space between the countersubstrate and the element substrate may be filled with an inert gas suchas dried nitrogen. Alternatively, a sealing material may be applied overthe entire surface of the pixel portion and then the counter substratemay be attached thereto. An ultraviolet curing resin or the like ispreferably used as the sealing material. A drying agent or a particlefor maintaining a constant gap between the substrates may be mixed inthe sealing material. Subsequently, a flexible wiring substrate isattached to the external connection portion.

Examples of structures of the light emitting device formed above will bedescribed with reference to FIGS. 12A and 12B. Further, portions havingsimilar functions are sometimes denoted by same reference numerals,though they have different shapes so as to omit explanation. In thisembodiment mode, the thin film transistor 70 having an LDD structure isconnected to the light emitting device 93 through the connection portion61 a.

FIG. 12A shows a structure where the anode 64 is formed using aconductive film having a light transmitting property, and lightgenerated in the light emitting stacked body 66 is emitted toward thesubstrate 50. Further, reference numeral 94 represents a countersubstrate. After forming the light emitting device 93 over the substrate50, the counter substrate is firmly attached to the substrate 50 using asealing material or the like. A space between the counter substrate 94and the light emitting device 93 is filled with a resin 88 having alight transmitting property or the like to seal the light emittingelement. Accordingly, the light emitting device 93 can be prevented frombeing deteriorated by moisture or the like. Preferably, the resin 88 hasa hygroscopic property. More preferably, to prevent the adverseinfluence of moisture, a drying agent 89 with a high light transmittingproperty is dispersed in the resin 88.

FIG. 12B shows a structure where both the anode 64 and the cathode 67are formed using conductive films having light transmitting propertiesand light can be emitted toward both the substrate 50 and the countersubstrate 94. In this structure, by providing polarizing plates 90outside of the substrate 50 and the counter substrate 94, a screen canbe prevented from being transparent, thereby improving visibility.Protection films 91 are preferably provided outside of the polarizingplates 90.

Further, arrangements of a transistor, a light emitting device, and thelike are not particularly limited. For example, they can be arranged asshown in a top view of FIG. 13. In FIG. 13, a first electrode of a firsttransistor 1001 is connected to a source signal line 1004 and a secondelectrode is connected to a gate electrode of a second transistor 1002.A first electrode of the second transistor is connected to a powersupply line 1005, and a second electrode of the second transistor isconnected to an electrode 1006 of a light emitting element. A part of agate signal line 1003 serves as a gate electrode of the first transistor1001.

The light emitting device according to the present invention with adisplay function may employ either analog video signals or digital videosignals. When using the digital video signals, light emitting displaydevices are classified into one in which the video signals use voltageand one in which the video signals use current. When light emittingdevices emit light, video signals input in pixels are classified intoone at constant voltage and one at constant current. The video signalsat constant voltage include one in which constant voltage is applied toa light emitting device and one in which constant current flows througha light emitting device. The video signals at constant current includeone in which constant voltage is applied to a light emitting device andone in which constant current flows though a light emitting device. Thecase where constant voltage is applied to a light emitting deviceindicates a constant voltage drive whereas the case where constantcurrent flows though a light emitting device indicates a constantcurrent drive. In the constant current drive, constant current flowsregardless of the change in resistance of a light emitting device. Thelight emitting device of the present invention and a method for drivingthe light emitting device may use either a driving method utilizingvoltage of video signals or a driving method utilizing current of videosignals. Furthermore, either the constant voltage drive or the constantcurrent drive may be used.

The life of the light emitting device of the present inventionmanufactured in accordance with the above described manufacturingmethod, is prolonged without deteriorating a characteristic thereof.Moreover, the present embodiment mode can be implemented by being freelycombined with any structure of the above described embodiment modes.

Embodiment Mode 8

An outer appearance of a panel which is a light emitting device of thepresent invention, will be described in this embodiment mode withreference to FIGS. 14A and 14B. FIG. 14A is a top view of a panel inwhich a transistor and a light emitting element formed over a substrateare sealed with a sealing material that is formed between the substrateand a counter substrate 4006. FIG. 14B is a cross sectional view along aline A-A′ of FIG. 14A. The light emitting device mounted on this panelhas a structure as shown in Embodiment Mode 7.

A sealing material 4005 is provided so as to surround a pixel portion4002, a signal line driver circuit 4003, and a scanning line drivercircuit 4004 that are provided over a substrate 4001. The countersubstrate 4006 is provided over the pixel portion 4002, the signal linedriver circuit 4003, and the scanning line driver circuit 4004. Thus,the pixel portion 4002, the signal line driver circuit 4003, and thescanning line driver circuit 4004 are hermetically sealed with thesubstrate 4001, the sealing material 4005, and the counter substrate4006 along with a filler 4007.

The pixel portion 4002, the signal line driver circuit 4003, and thescanning line driver circuit 4004, which are provided over the substrate4001, have a plurality of thin film transistors. In FIG. 14B, a thinfilm transistor 4008 included in the signal line driver circuit 4003 anda thin film transistor 4010 included in the pixel portion 4002 areshown.

Further, a light emitting device 4011 is electrically connected to thethin film transistor 4010.

Also, a leading wiring 4014 corresponds to a wiring for supplyingsignals or power supply voltage to the pixel portion 4002, the signalline driver circuit 4003, and the scanning line driver circuit 4004. Theleading wiring 4014 is connected to a connection terminal 4016 through aleading wiring 4015 a and a leading wiring 4015 b. The connectionterminal 4016 is electrically connected to a terminal included in aflexible printed circuit (FPC) 4018 through an anisotropic conductivefilm 4019.

Further, as the filler 4007, an ultraviolet curing resin or a heatcuring resin can be used in addition to an inert gas such as nitrogenand argon. For example, polyvinyl chloride, acrylic, polyimide, an epoxyresin, a silicon resin, polyvinyl butyral, or ethylene vinylene acetatecan be used.

Furthermore, a light emitting device of the present invention includes apanel in which a pixel portion having a light emitting device is formedand a module in which an IC is mounted on the panel.

In the light emitting device having such a structure, generation of darkspots can be suppressed without increasing driving voltage and powerconsumption.

This embodiment mode can be implemented by being combined with the aboveembodiment modes.

Embodiment Mode 9

Pixel circuits and protection circuits included in the panel and moduledescribed in Embodiment Mode 8, and operations thereof will be describedin this embodiment mode. Further, the cross sectional views as shown inFIGS. 10A to 10E and FIGS. 11A to 11C correspond to cross sectionalviews of a driving TFT 1403 and a light emitting device 1405.

In a pixel as shown in FIG. 15A, a signal line 1410, power supply lines1411 and 1412 are arranged in columns, whereas a scanning line 1414 isarranged in a row. The pixel also includes a switching TFT 1401, adriving TFT 1403, a current controlling TFT 1404, a capacitor element1402, and a light emitting device 1405.

A pixel as shown in FIG. 15C has a similar structure to the one shown inFIG. 15A, except that a gate electrode of the driving TFT 1403 isconnected to a power supply line 1412 that is arranged in a row. Thatis, both pixels depicted in FIGS. 15A and 15C show similar equivalentcircuit diagrams. However, respective power supply lines are formed ofconductive films in different layers between the case where the powersupply line 1412 is arranged in a column (FIG. 15A) and the case wherethe power supply line 1412 is arranged in a row (FIG. 15C). In order toemphasis on the different arrangements of the power supply lines towhich the gate electrodes of the driving TFTs 1403 are connected, theequivalent circuit diagrams are individually illustrated in FIGS. 15Aand 15C.

In each pixel as shown in FIGS. 15A and 15C, the driving TFT 1403 andthe current controlling TFT 1404 are connected in series in each pixel,and the channel length L(1403) and the channel width W(1403) of thedriving TFT 1403 and the channel length L(1404) and the channel widthW(1404) of the current controlling TFT 1404 may be set to satisfy therelation of L(1403)/W(1403): L(1404)/W(1404)=5 to 6,000:1.

The driving TFT 1403 is operated in a saturation region and controls theamount of current flowing through the light emitting element 1405,whereas the current controlling TFT 1404 is operated in a linear regionand controls current supplied to the light emitting device 1405. Theboth TFTs 1403 and 1404 preferably have a same conductivity type in viewof the manufacturing process, and n-channel TFTs are formed as the TFTs1403 and 1404 in this embodiment mode. Also, a depletion type TFT may beused as the driving TFT 1403 instead of an enhancement type TFT. In alight emitting device of the present invention having the abovestructure, slight variations in V_(gs) of the current controlling TFT1404 does not adversely affect the amount of current flowing through thelight emitting device 1405, since the current controlling TFT 1404 isoperated in the linear region. That is, the amount of current flowingthrough the light emitting device 1405 can be determined by the drivingTFT 1403 operated in the saturation region. In accordance with the abovedescribed structure, it is possible to provide a light emitting devicein which image quality is improved by improving variations in luminanceof a light emitting element due to variation of the TFT characteristics.

The switching TFT 1401 of each pixel as shown in FIGS. 15A to 15Dcontrols a video signal input with respect to the pixel. When theswitching TFT 1401 is turned on and a video signal is input in thepixel, a voltage of the video signal is held in the capacitor element1402. Although the arrangement in which each pixel includes thecapacitor element 1402 are shown in FIGS. 15A and 15C, the presentinvention is not limited thereto. When a gate capacitor or the like canserve as a capacitor for holding a video signal, the capacitor element1402 may not be provided.

A pixel as shown in FIG. 15B has a similar structure to the one shown inFIG. 15A, except that a TFT 1406 and a scanning line 1415 are addedthereto. Similarly, a pixel as shown in FIG. 15D has a similar structureto the one shown in FIG. 15C, except that a TFT 1406 and a scanning line1415 are added thereto.

The TFT 1406 is controlled to be turned on/off by the newly providedscanning line 1415. When the TFT 1406 is turned on, the charge held inthe capacitor element 1402 is discharged, thereby turning the currentcontrolling TFT 1404 off. That is, supply of current flowing through thelight emitting element 1405 can be forcibly stopped by providing the TFT1406. Therefore, the TFT 1406 can also referred to as an erasing TFT. Alighting period can start simultaneously with or immediately after awriting period starts before signals are written into all the pixels inaccordance with the structures shown in FIGS. 15B and 15D, and hence,the duty ratio can be improved.

In a pixel as shown in FIG. 15E, a signal line 1410 and a power supplyline 1411 are arranged in columns while a scanning line 1414 is arrangedin a row. The pixel further includes a switching TFT 1401, a driving TFT1403, a capacitor element 1402, and a light emitting element 1405. Apixel shown in FIG. 15F has a similar structure to the one shown in FIG.15E, except that a TFT 1406 and a scanning line 1415 are added thereto.Further, the structure as shown in FIG. 15F also allows a duty ratio tobe improved by providing the TFT 1406.

As described above, various kinds of pixel circuits can be employed. Inparticular, when a thin film transistor is formed using an amorphoussemiconductor film, an area of a semiconductor film of the driving TFT1403 is preferably made large. Therefore, in the above pixel circuits, atop emission type in which light generated in the light emitting stackedbody is emitted through a sealing substrate, is preferably employed.

It is thought that such an active matrix light emitting device ispreferable when pixel density is increased since a TFT is provided foreach pixel.

An active matrix light emitting device in which a TFT is provided ineach pixel is described in this embodiment mode. However, a passivematrix light emitting device in which a TFT is provided for each columncan be formed. Since a TFT is not provided in each pixel in the passivematrix light emitting device, high aperture ratio is obtained. In thecase of a light emitting device in which light generated in a lightemitting stacked body is emitted toward both sides of the light emittingstacked body, when a passive matrix light emitting device is employed,transmittance can be increased.

In a light emitting device of the present invention further having suchpixel circuits, a material, which is suitable for a structure and aperformance to be required of the light emitting device, can be used asan electrode of the light emitting device. In addition, the lightemitting device can have the above described characteristics.

Subsequently, a case in which diodes are provided as protection circuitsin a scanning line and a signal line, will be described using anequivalent circuit shown in FIG. 15E.

In FIG. 16, switching TFTs 1401 and 1403, a capacitor element 1402, anda light emitting device 1405 are provided in a pixel portion 1500. Inthe signal line 1410, diodes 1561 and 1562 are provided. The diodes 1561and 1562 are manufactured in accordance with the above describedembodiment mode as well as the switching TFTs 1401 and 1403. Each diodeincludes a gate electrode, a semiconductor layer, a source electrode, adrain electrode, and the like. By connecting the gate electrode to thedrain electrode or the source electrode, the diodes 1561 and 1562 areoperated.

Common potential lines 1554 and 1555 connecting to the diodes 1561 and1562 are formed in the same layer as the gate electrodes. Therefore, itis necessary to form contact holes in a gate insulating layer so as tobe in contact with the source electrodes or the drain electrodes of thediodes.

Diodes 1563 and 1564 provided in the scanning line 1414 has the similarstructure.

As mentioned above, protection diodes can be simultaneously formed in aninput stage according to the present invention. Further, the positionsof the protection diodes are not limited thereto, and they can beprovided between a driver circuit and a pixel.

A light emitting device of the present invention including suchprotection circuits has high reliability since it can be driven for longtime. Further, the reliability of the light emitting device can befurther improved by employing the above described structure.

Embodiment Mode 10

As electronic appliances having light emitting devices according to thepresent invention mounted with modules as shown in the above embodimentmode, a camera such as a video camera and a digital camera; a goggletype display (a head mounted display); a navigation system; an audioreproducing device (e.g., a car audio component); a computer; a gamemachine; a portable information terminal (e.g., a mobile computer, amobile phone, a portable game machine, an electronic book, and thelike); an image reproducing device equipped with a recording medium(concretely, a device having a display that can reproduce a recordingmedium such as a digital versatile disc (DVD) and can display an imagethereof); and the like can be given. Specific examples of theseelectronic appliances are shown in FIGS. 17A to 17E, and FIGS. 18A and18B.

FIG. 17A shows a monitor for a television receiver, a personal computer,or the like, including a housing 3001, a display portion 3003, speakers3004, and the like. An active matrix display device is provided in thedisplay portion 3003. Each pixel of the display portion 3003 includes alight emitting device formed by using the manufacturing method of thepresent invention and a TFT. By using the light emitting device of thepresent invention, a television having long light emitting life alongwith less deterioration in characteristics can be obtained.

FIG. 17B shows a mobile phone, including a main body 3101, a housing3102, a display portion 3103, an audio input portion 3104, an audiooutput portion 3105, operation keys 3106, an antenna 3108, and the like.An active matrix display device is provided in the display portion 3103.Each pixel of the display portion 3103 includes a light emitting deviceformed by using the manufacturing method of the present invention and aTFT. By using the light emitting device of the present invention, amobile phone having long light emitting life along with lessdeterioration in characteristics can be obtained.

FIG. 17C shows a computer, including a main body 3201, a housing 3202, adisplay portion 3203, a keyboard 3204, an external connection port 3205,a pointing mouse 3206, and the like. An active matrix display device isprovided in the display portion 3203. Each pixel of the display portion3203 includes a light emitting device formed by using the manufacturingmethod of the present invention and a TFT. By using the light emittingdevice of the present invention, a computer having long light emittinglife along with less deterioration in characteristics can be obtained.

FIG. 17D shows a mobile computer, including a main body 3301, a displayportion 3302, a switch 3303, operation keys 3304, an infrared port 3305,and the like. An active matrix display device is provided in the displayportion 3302. Each pixel of the display portion 3302 includes a lightemitting device formed by using the manufacturing method of the presentinvention and a TFT. By using the light emitting device of the presentinvention, a mobile computer having long light emitting life along withless deterioration in characteristics can be obtained.

FIG. 17E shows a portable game machine, including a housing 3401, adisplay portion 3402, speaker portions 3403, operation keys 3404, arecording medium insert portion 3405, and the like. An active matrixdisplay device is provided in the display portion 3402. Each pixel ofthe display portion 3402 includes a light emitting device formed byusing the manufacturing method of the present invention and a TFT. Byusing the light emitting device of the present invention, a portablegame machine having long light emitting life along with lessdeterioration in characteristics can be obtained.

FIG. 18A shows a flexible display, including a main body 3110, a pixelportion 3111, a driver IC 3112, a receiving apparatus 3113, a filmbuttery 3114, and the like. The receiving apparatus 3113 can receive asignal from an infrared communication port 3107 of the above describedmobile phone. An active matrix display device is provided in the pixelportion 3111. Each pixel of the pixel portion 3111 includes a lightemitting device formed by using the manufacturing method of the presentinvention and a TFT. By using the light emitting device of the presentinvention, a flexible display having long light emitting life along withless deterioration in characteristics can be obtained.

FIG. 18B shows an ID card manufactured according to the presentinvention, including a supporting body 5541, a display portion 5542, onintegrated circuit chip 5543 incorporated in the supporting body 5541,and the like.

An active matrix display device is provided in the display portion 5542.Each pixel of the display portion 5542 includes a light emitting deviceformed using the manufacturing method of the present invention and aTFT. By using the light emitting device of the present invention, an IDcard having long light emitting life along with less deterioration incharacteristics can be obtained.

As set forth above, an application range of the present invention isextremely wide, and the present invention can be applied to electronicappliances in all fields.

Embodiment

Changes in luminance with time passage of a light emitting device, inwhich a mixed layer was formed using DNTPD as an organic compound, metaloxide as molybdenum trioxide, and rubrene, which is a substance withlarge steric hindrance, the mixed layer was exposed to an nitrogenatmosphere, and then a hole transporting layer, a light emitting layer,an electron transporting layer, an electron injecting layer, and acathode were formed; and changes in luminance with time passage of alight emitting device, in which a mixed layer was not exposed to thenitrogen gas atmosphere, were measured in this embodiment.

An anode 2 was formed using ITO over a glass substrate 1, and then theglass substrate was heated under reduced pressure at 150° C. for 30minutes (FIGS. 1A and 1B). Next, a mixed layer 3 was formed underreduced pressure to have a thickness of 120 nm by co-evaporation ofDNTPD, molybdenum trioxide, and rubrene (FIG. 1C). DNTPD, molybdenumtrioxide, and rubrene were mixed to satisfy DNTPD:molybdenumtrioxide:rubrene=1:0.5:0.02 (mass ratio). Thereafter, the mixed layer 3was exposed to a nitrogen gas atmosphere at a room temperature underatmospheric pressure overnight without being exposed to a gas atmosphereincluding oxygen (FIG. 1D). Further, the moisture content of thenitrogen gas was about 0.5 ppm.

Subsequently, without exposing the mixed layer 3 to a gas atmosphereincluding oxygen, a hole transporting layer 4 was formed using NPB byevaporation under reduced pressure to have a thickness of 10 nm (FIG.19). A light emitting layer 5 was formed using Alq₃ as a host materialand DMQd as a dopant material by evaporation to have a thickness of 37.5nm (FIG. 19). A weight ratio between Alq₃ and DMQd was set to be 1:1.003(=Alq₃:DMQd).

An electron transporting layer 6 was formed under reduced pressure usingAlq₃ by evaporation to have a thickness of 37.5 nm. Next, an electroninjecting layer 16 was formed under reduced pressure using CaF₂ to havea thickness of 1 nm. A cathode 7 was formed under reduced pressure usingAl to have a thickness of 200 nm. Thus, a light emitting device 1 wasmanufactured (FIG. 19).

Meanwhile, a light emitting device 2, in which after forming a mixedlayer 3, a light emitting layer, an electron transporting layer, anelectron injecting layer, and a cathode were formed without exposing themixed layer 3 to the nitrogen atmosphere, was manufactured as acomparative example. The light emitting device 2 was manufactured in thesimilar manner as the light emitting device 1 with the exception thatthe mixed layer 3 was not exposed to the nitrogen gas atmosphere.

FIG. 20 is a graph showing measurement results of changes in luminancewith time passage of the light emitting devices 1 and 2 manufactured inthis embodiment. In FIG. 20, reference numeral 1 indicates the lightemitting device 1 and reference numeral 2 indicates the light emittingdevice 2. In FIG. 20, a horizontal axis indicates time passage (hour)whereas a vertical axis indicates light emitting luminance. The lightemitting luminance was shown by a value relative to initial luminance ina case where the initial luminance was set to be 100. Note that thismeasurement was carried out by a method where current with a constantcurrent density was continuously fed to each of the light emittingdevices and luminance of each of the light emitting devices was measuredfor given time. The current density used a value when the initialluminance become 3,000 cd/m².

In a case where time when the luminance become 70 as compared with theinitial luminance (100) was set to be light emitting life, it was knownthat the light emitting life of the light emitting device 2 was 530hours whereas the light emitting life of the light emitting device 1 was710 hours. Therefore, the light emitting life of the light emittingdevice 1 was increased by 1.3 times by exposing the mixed layer 3 to thenitrogen gas atmosphere.

This application is based on Japanese Patent Application Serial No.2005-194559 filed in Japan Patent Office on Jul. 4, 2005, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A method for manufacturing a light emittingdevice, comprising: forming an anode; forming a hole transporting layerover the anode; forming a light emitting layer over the holetransporting layer; forming an electron transporting layer over thelight emitting layer; forming a mixed layer including a first organiccompound, a second organic compound, and metal oxide over the electrontransporting layer by a co-evaporation in vacuum; after forming themixed layer step, exposing the mixed layer to a nitrogen gas atmospherewithout exposing the mixed layer to a gas atmosphere including oxygen;and after exposing step, forming a cathode over the mixed layer withoutexposing the mixed layer to a gas atmosphere including oxygen.
 2. Themethod for manufacturing a light emitting device according to claim 1,wherein an electron injecting layer is formed between the mixed layerand the electron transporting layer.
 3. The method for manufacturing alight emitting device according to claim 1, wherein after the mixedlayer is exposed to the nitrogen gas atmosphere, the nitrogen gas isevacuated, and the mixed layer is exposed to a nitrogen gas atmosphereagain.
 4. The method for manufacturing a light emitting device accordingto claim 1, wherein the mixed layer is sprayed with the nitrogen gas tobe exposed to the nitrogen gas atmosphere.
 5. The method formanufacturing a light emitting device according to claim 1, wherein thefirst organic compound comprises a carbazole group, and wherein thesecond organic compound is a compound providing steric hindrance to themixed layer.
 6. The method for manufacturing a light emitting deviceaccording to claim 1, wherein the first organic compound is representedby general formula (1),

wherein R¹ and R³ independently represents any of hydrogen, an alkylgroup having 1 to 6 carbon atoms, an aryl group having 6 to 25 carbonatoms, a heteroaryl group having 5 to 9 carbon atoms, an arylalkylgroup, and an acyl group having 1 to 7 carbon atoms, wherein Ar¹represents an aryl group having 6 to 25 carbon atoms or a heteroarylgroup having 5 to 9 carbon atoms, wherein R² represents any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, and an aryl grouphaving 6 to 12 carbon atoms, wherein R⁴ represents any one of hydrogen,an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12carbon atoms, and a substituent represented by a general formula (2),

wherein R⁵ represents any one of hydrogen, an alkyl group having 1 to 6carbon atoms, an aryl group having 6 to 25 carbon atoms, a heteroarylgroup having 5 to 9 carbon atoms, an arylalkyl group, and an acyl grouphaving 1 to 7 carbon atoms, wherein Ar² represents an aryl group having6 to 25 carbon atoms or a heteroaryl group having 5 to 9 carbon atoms,wherein R⁶ represents any one of hydrogen, an alkyl group having 1 to 6carbon atoms, and an aryl group having 6 to 12 carbon atoms, and whereinthe second organic compound is a compound providing steric hindrance tothe mixed layer.
 7. A method for manufacturing a light emitting device,comprising: forming a mixed layer including a first organic compound, asecond organic compound, and metal oxide over a substrate by aco-evaporation in vacuum; after forming the mixed layer step, exposingthe mixed layer to a nitrogen gas atmosphere without exposing the mixedlayer to a gas atmosphere including oxygen; and after exposing step,forming a next layer without exposing the mixed layer to a gasatmosphere including oxygen over the mixed layer.
 8. The method formanufacturing a light emitting device according to claim 7, whereinafter the mixed layer is exposed to the nitrogen gas atmosphere, thenitrogen gas is evacuated, and the mixed layer is exposed to a nitrogengas atmosphere again.
 9. The method for manufacturing a light emittingdevice according to claim 7, wherein the mixed layer is sprayed with thenitrogen gas to be exposed to the nitrogen gas atmosphere.
 10. Themethod for manufacturing a light emitting device according to claim 7,wherein the first organic compound comprises a carbazole group, andwherein the second organic compound is a compound providing sterichindrance to the mixed layer.
 11. The method for manufacturing a lightemitting device according to claim 7, wherein the first organic compoundis represented by general formula (1),

wherein R¹ and R³ independently represents any of hydrogen, an alkylgroup having 1 to 6 carbon atoms, an aryl group having 6 to 25 carbonatoms, a heteroaryl group having 5 to 9 carbon atoms, an arylalkylgroup, and an acyl group having 1 to 7 carbon atoms, wherein Ar¹represents an aryl group having 6 to 25 carbon atoms or a heteroarylgroup having 5 to 9 carbon atoms, wherein R² represents any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, and an aryl grouphaving 6 to 12 carbon atoms, wherein R⁴ represents any one of hydrogen,an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12carbon atoms, and a substituent represented by a general formula (2),

wherein R⁵ represents any one of hydrogen, an alkyl group having 1 to 6carbon atoms, an aryl group having 6 to 25 carbon atoms, a heteroarylgroup having 5 to 9 carbon atoms, an arylalkyl group, and an acyl grouphaving 1 to 7 carbon atoms, wherein Ar² represents an aryl group having6 to 25 carbon atoms or a heteroaryl group having 5 to 9 carbon atoms,wherein R⁶ represents any one of hydrogen, an alkyl group having 1 to 6carbon atoms, and an aryl group having 6 to 12 carbon atoms, and whereinthe second organic compound is a compound providing steric hindrance tothe mixed layer.
 12. A method for manufacturing a light emitting device,comprising: forming an anode; forming a first mixed layer including afirst organic compound, a second organic compound, and a metal oxideover the anode; forming a light emitting layer over the first mixedlayer; forming a second mixed layer including the first organiccompound, the second organic compound, and the metal oxide over thelight emitting layer by a co-evaporation in vacuum; and forming acathode over the second mixed layer, wherein the first mixed layer isexposed to a nitrogen gas atmosphere without exposing the first mixedlayer to a gas atmosphere including oxygen after forming the first mixedlayer and before forming the light emitting layer, and wherein thesecond mixed layer is exposed to a nitrogen gas atmosphere withoutexposing the second mixed layer to a gas atmosphere including oxygenafter forming the second mixed layer and before forming the cathode. 13.The method for manufacturing a light emitting device according to claim12, wherein after each of the first mixed layer and the second mixedlayer is exposed to the nitrogen gas atmosphere, the nitrogen gas isevacuated, and each of the first mixed layer and the second mixed layeris exposed to a nitrogen gas atmosphere again.
 14. The method formanufacturing a light emitting device according to claim 12, whereineach of the first mixed layer and the second mixed layer is sprayed withthe nitrogen gas to be exposed to the nitrogen gas atmosphere.
 15. Themethod for manufacturing a light emitting device according to claim 12,wherein the first organic compound comprises a carbazole group, andwherein the second organic compound is a compound providing sterichindrance to the first mixed layer and the second mixed layer.
 16. Themethod for manufacturing a light emitting device according to claim 12,wherein the first organic compound is represented by general formula(1),

wherein R¹ and R³ independently represents any of hydrogen, an alkylgroup having 1 to 6 carbon atoms, an aryl group having 6 to 25 carbonatoms, a heteroaryl group having 5 to 9 carbon atoms, an arylalkylgroup, and an acyl group having 1 to 7 carbon atoms, wherein Ar¹represents an aryl group having 6 to 25 carbon atoms or a heteroarylgroup having 5 to 9 carbon atoms, wherein R² represents any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, and an aryl grouphaving 6 to 12 carbon atoms, wherein R⁴ represents any one of hydrogen,an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12carbon atoms, and a substituent represented by a general formula (2),

wherein R⁵ represents any one of hydrogen, an alkyl group having 1 to 6carbon atoms, an aryl group having 6 to 25 carbon atoms, a heteroarylgroup having 5 to 9 carbon atoms, an arylalkyl group, and an acyl grouphaving 1 to 7 carbon atoms, wherein Ar² represents an aryl group having6 to 25 carbon atoms or a heteroaryl group having 5 to 9 carbon atoms,wherein R⁶ represents any one of hydrogen, an alkyl group having 1 to 6carbon atoms, and an aryl group having 6 to 12 carbon atoms, and whereinthe second organic compound is a compound providing steric hindrance tothe first mixed layer and the second mixed layer.